During 1869 in Texas, rancher Jim Coates (Fess Parker) prepares to leave his wife, Katie (Dorothy McGuire), and their two sons, teenaged Travis (Tommy Kirk) and young Arliss (Kevin Corcoran), for a four-month cattle drive. After Katie bids him a tearful goodbye, he tells Travis that he must now assume responsibility as man of the house, promising to reward him with a horse upon his return.
The next day, he is working the small corn field with Jumper, the family mule, when a stray dog chases a rabbit into the field. Jumper, spooked, rears and runs, ruining the crops and felling the fence. Travis is furious with him, and grows even more angry that night when he eats some of their meat. Despite Travis' attempt to beat him, which he dubs "Old Yeller" (Spike), Arliss falls in love with him and Katie, who hopes he will protect him, welcomes him into the family. The next afternoon, returning home with a deer for dinner, Travis spots him in the drinking-water pond and throws stones at him, prompting Arliss to attack his brother and Travis to dislike him even more. That night, he hangs the venison low in an attempt to entice him into stealing it, so he can banish him the next day. He is shocked when he spends the night guarding it without touching it. Later, Arliss traps a bear cub, and when the mother bear charges him, Travis and Katie witness Old Yeller leap to his protection, fighting off the much larger animal. That night, Travis, finally impressed with him, allows him into their bed.
Soon after, neighbor Bud Searcy (Jeff York) visits with his daughter, Lisbeth (Beverly Washburn), who has a crush on Travis. Katie tolerates him despite his extreme laziness and tendency to brag, offering him dinner when he refuses to leave.
While helping Travis pick corn, Lisbeth reveals that she saw Old Yeller stealing food from neighboring farms, but will never report him because he has impregnated hers, Miss Prissy. Pleased, Travis gives her an arrowhead, which she treasures, and determines to keep Old Yeller with him at all times, to prevent him from stealing. That night, he sleeps out in the field with Old Yeller, hoping to catch the raccoons that have been eating the corn. He falls asleep while thinking of his father, but wakes to see Old Yeller faithfully chasing off a raccoon family. In the morning, Katie informs him that their cow, Rose, is missing and has probably given birth in the hills. He and Old Yeller set off to find her but when he discovers the newborn calf and tries to carry it, she charges him, prompting Old Yeller to knock her over until she calms down. At home, he attempts to break her, but can't until she spots Old Yeller and becomes docile. Having proven his mettle beyond a doubt, Old Yeller becomes his constant, devoted companion.
One day, cowhand Burn Sanderson (Chuck Connors) arrives, revealing that Old Yeller is his dog. Although Travis is devastated, Katie knows she must let Burn take him. As he leaves, however, Arliss explodes in anger, throwing a rock that makes Burn's horse rear and throw him. He is at first angry but then takes Arliss on his knee and agrees to trade Old Yeller for one horned toad and a home-cooked meal, which Katie supplies with pleasure. Upon leaving, he informs Travis that a plague of hydrophobia, or rabies, is affecting local animals, with telltale signs that include staggering, viciousness, and unprovoked attacks.
Later, Travis takes Old Yeller, and they follow wild pig tracks until they find a herd. Old Yeller ably corners the pigs, allowing Travis to climb a tree and swing a lasso down to rope one. When it falls, however, it pulls him down from the tree, where a boar bites him in his leg. Old Yeller swiftly attacks it so Travis can run to safety, but Old Yeller is severely wounded in the process. Travis hides him in a cave and limps home, where Katie dresses his wound and at first refuses to let him return to Old Yeller. When she sees his distress, however, she relents, and takes him by horseback to find Old Yeller, who is already being circled by buzzards. Although his wounds are deep, she tends to him and brings both home to recuperate.
Soon after, the Searcys visit. Lisbeth presents Travis with one of Old Yeller's puppies, but, unimpressed, he hurts her feelings by telling her to give it to Arliss. Bud then informs Katie about the rabies plague, terrifying her that Travis may have been infected and prompting her to demand that he leave. He does, but leaves Lisbeth behind "to help". Days later, Travis is nearly recovered when Rose falls in a fit. Katie hopes it is a mere fever, but Travis recognizes the symptoms as those of rabies, and shoots her, after which Katie and Lisbeth burn the carcass. When a wolf attacks, their screams alert Travis, who runs outside with a gun and sees Old Yeller fighting it off. Travis is able to shoot it, but not before it bites Old Yeller, and Katie sadly informs him that the wolf, which attacked without provocation, was mad. At his pleading, she agrees to keep Old Yeller penned in the corn crib for a few weeks to chart his progress, hoping he will remain unaffected. At first he seems healthy, but one night he growls viciously at Travis, who tries to hide the affliction from the family.
When Arliss attempts to release him, however, Katie closes the crib just in time and sees that he is ill. She prepares to shoot him, but Travis insists on handling the terrible chore himself. His rifle shaking, he finally manages to shoot his friend, putting him out of his misery. The next day, Jim returns home. After greeting an elated Katie and Arliss, he approaches Travis, advising him to start looking for something good to take the place of the bad turn life has dealt him.
Although Travis remains despondent, when the family retires for dinner, he notices Old Yeller's puppy attempting to steal venison. Recognizing his strong resemblance to his father, Travis admires him for the first time, and in return he licks his face joyfully.
Differences from the book
- The only major difference between the book and the film is that in the book, Katie convinces Travis to shoot Old Yeller shortly after he fights with the wolf and is exposed to rabies (during the incubation period), whereas in the film, he insists on waiting until he develops symptoms before killing him. In the book Travis and Old Yeller had not fully recovered from the wounds they received from the hogs. Katie and Lisbeth had gone to burn Rose's carcass and return being chased by the rabid wolf which is kept at bay by Old Yeller. Travis shoots it as it is about to kill him but in a cruel twist of fate is then forced to shoot him because he has been exposed to rabies and will eventually become a deadly threat to the family. There is also the minor difference in that Old Yeller is bob-tailed in the book. Whereas, in the movie, he has a long tail that arches over his back (similar to the tails of Arctic sled dogs). Another major difference is that he appears as a Lab/Mastiff mix, while in the book he is implied to be a Blackmouth Cur.
- Tommy Kirk: Travis Coates, the film's protagonist. A 14-year-old boy who wants a man's horse.
- Spike: Old Yeller, the title character of the story. A Mastador (Labrador Retriever/English Mastiff mix) who fights animals who belonged to Burn Sanderson and Travis' and Arliss' loyal dog.
- Kevin Corcoran: Arliss Coates, the film's tritagonist. A 5-year-old boy who wants to be good a hunter as Travis since he's Arliss' older brother.
- Fess Parker: Jim Coates, Travis' and Arliss' father who goes to Kansas and comes home with presents for his family especially the horse for Travis.
- Dorothy McGuire: Katie Coates, Travis' and Arliss' mother who likes Old Yeller a lot.
- Jeff York: Bud Searcy, a man who treats Lisbeth, Travis, and Arliss like slaves.
- Beverly Washburn: Lisbeth Searcy, Bud's daughter who Travis is in love with.
- Chuck Connors: Burn Sanderson, Old Yeller's original whom he ran away from.