The plot centers around a young man who is given a cute, furry little animal as a pet. To his surprise, the animal reproduces when it is splashed with water. Its children later transform into dangerous monsters that threaten the small town of Kingston Falls on Christmas Eve.
A sequel, Gremlins 2: The New Batch, was released in 1990.
One evening in December, inventor Randall Peltzer is wandering around New York City's Chinatown, looking for a Christmas present for his son. A young boy leads him to his grandfather's small cluttered shop. Mr. Peltzer does not see anything that he wants to buy in the shop, until he hears singing coming from a small cage. He finds that the singing is coming from a small furry animal called a Mogwai. Mr. Peltzer offers to pay any price for the Mogwai but the elderly Chinese store-owner refuses to sell, saying that owning a Mogwai is to great a responsibility. However, the boy agrees to sell the Mogwai to Mr. Peltzer later, saying that his family needs the money. He tells Mr. Peltzer three important rules for keeping a Mogwai: Keep it away from bright lights. Sunlight will kill it. Never get it wet. Never feed it after midnight.
Mr. Peltzer returns home to Kingston Falls and gives the Mogwai, which he has named Gizmo, to his son Billy, a young bank clerk and aspiring cartoonist. When a glass of water is accidentally spilled on Gizmo, it immediately produces five more Mogwais. One, known as Stripe because of the Mohican-like white crest on his head, quickly sets himself up as the leader of the little Mogwais. Billy takes Gizmo to his old science teacher Mr.Hanson. He produces a sixth Mogwai which he leaves with the teacher.
The five little Mogwais trick Billy into feeding them after midnight by stopping his clock. They then transform into cocoons. Gizmo, who refused the food, remains unchanged. The Mogwai left with Mr. Hanson transforms also. When the creatures hatch out of the cocoons they are transformed into reptile-like monsters known as gremlins. The gremlin's attack Billy's mother but, with Billy's help, she fights them off and kills most of them. Stripe, however, escapes. He jumps into a swimming pool thus creating hundreds more gremlins. The gremlins head into town and cause chaos.
The bar where Billy's girlfriend, Kate Beringer, works is overrun by gremlins. With the help of Billy and Gizmo, she is able to escape. All of the gremlins then head to the local movie theater and watch a reel of Snow White and the Seven Dwarfs. Billy and Kate set off an explosion that kills most of the gremlins but Stripe escapes again.
Stripe goes into a nearby department store. He jumps into a fountain, beginning to produce more gremlins. However, dawn is approaching. The blinds are opened and, in a scene based on the finale of the 1958 movie The Horror of Dracula, Stripe is killed by the sunlight.
While Kate and the Peltzers are recovering at Billy's home, the elderly Chinese store-owner arrives. He sees the chaos that the gremlins caused on the television news, confirming his opinion that people are not ready for the responsibility of owning a Mogwai. However, before he leaves, he tells Billy that he may one day be ready for that responsibility.
- Billy Peltzer (Zach Galligan), the owner of Gizmo and the film's protagonist.
- Gizmo (voiced by Howie Mandel), the Mogwai and the deurteragonist.
- Kater Beringer (Phoebe Kates), Billy's love interest and the film's tritagonist.
- Randy Peltzer (Hoyt Axton), Billy's father.
- Stripe (voiced by Frank Welker), the leader of the Gremlins and the main antagonist.
- Mrs. Deagle (Polly Holliday), the strict bank owner and the main human antagonist.
- Mr. Hansen (Glynn Turman), the science teacher
- Lynn Peltzer (Frances Lee McCain), Billy's mother.
- Pete Fountaine (Corey Feldman), Billy's child friend.
- Murray Futterman (Dick Miller), Billy's friend.
- Sheila Futterman (Jackie Joseph), Murray's wife.
- Sheriff Frank (Scott Brady), the sheriff.
- Mr. Wing (Keye Luke), the original owner of Gizmo.
- Deputy Brent (Jonathan Banks), Frank's assistant.
- Mrs. Harris (Belinda Balaski), a starving woman with children.
- ↑ In modern Mandarin Chinese, "Mogwai" is the name of the Devil.
- ↑ The word "gremlin" was first used by pilots in Britain's RAF in the 1920s. It originally referred to a mythical creature that caused airplanes to malfunction. The meaning was later expanded so that malfunctioning machines of any kind were blamed on "gremlins".