鼠形亚目（学名Myomorpha），啮齿目中最大的一个亚目，包含了将近25%的哺乳类物种，它们的外表皆与老鼠相似。

以前，鼠形亚目也包括下列一个或两个的总科。

The suborder Myomorpha contains 1,137 species of mouse-like rodents, nearly a quarter of all mammal species. Included are mice, rats, gerbils, hamsters, lemmings and voles. They are grouped according to the structure of their jaws and molar teeth. Both their medial and lateral masseter muscles are displaced forward, making them adept at gnawing. The medial masseter muscle goes through the eye socket, a feature unique among mammals. Myomorphs are found worldwide (apart from Antarctica) in almost all land habitats. They are usually nocturnal seed-eaters.