Nobita saves a drowning puppy by chance, names him "Ichi" and brings him home without his mother's knowledge. One day, while traveling in the mountains, Nobita discovers that there are a lot of abandoned cats and dogs in the mountains. For the sake of these abandoned cats and dogs, Nobita and Doraemon used the shrinking lamp to shrink the kittens and dogs and then boarded a time travel machine, heading for the world 300 million years ago when human beings had not yet been born, but suddenly, their flight time was swept into a time warp

Because of the time warp, Doraemon, Nobita, and his friends couldn't go back to 300 million years ago to see Ichi, and instead, they came to the civilization of the advanced cat and dog country by mistake. The dog and cat country is a civilized and advanced country.

Doraemon meets Sammy, a singer, at a restaurant in the Land of Dogs and Cats, and falls in love with her at first sight. Doraemon also meets Hachi, a dog that resembles Ichi, and befriends Toku, Chiko and Butaro. In order to help Hachi to find his missing parents, Nobita and the others go to the Chalu Cat amusement park to investigate. However, the person in charge of the amusement park, Chalu Cat, is very treacherous and has prepared a trap to deal with Nobita and Hachi.