小家鼠（学名Mus musculus）也称为家鼠、鼷鼠或小鼠。

小家鼠体长约8厘米，尾巴略短或略长于体长；毛色变化大，从黑灰色到灰褐色，腹毛基部为灰色，尖端常为灰黄色，有的呈灰白色，有的腹毛全白，足为暗褐色，也有的白色；尾上下两色。

The house mouse (Mus musculus) is a small mammal of the order Rodentia, characteristically having a pointed snout, small rounded ears, and a long naked or almost hairless tail. It is one of the most numerous species of the genus Mus. Although a wild animal, the house mouse mainly lives in association with humans.