The plural form of “mouse,” meaning the small animal, is “mice.” This is an irregular English plural: instead of adding -s or -es, the vowel changes from the long “ou” sound in mouse to the “ī” sound in mice.
The pattern is inherited from Old English, where some nouns formed plurals through a vowel change known as an apophonic or mutated plural. Other familiar examples include goose and geese, foot and feet, and tooth and teeth. These forms are remnants of older Germanic language patterns.
“Mices” and “mouses” are not the standard modern plurals for the animal. “Meese” is generally humorous or mistaken when referring to mice; it is sometimes used jokingly for moose, whose ordinary plural is usually “moose.”
The word “mouse” can also mean a computer pointing device, creating a small distinction in technical writing. Dictionaries commonly accept both “mice” and “mouses” for computer devices, although “mice” is more common. For the animal, however, standard English uses only “mice.”