Laimosemion is a genus of fish in the family Rivulidae from the Amazon basin and basins in the Guiana Shield in tropical South America. They mostly inhabit small streams, creeks, swamps and pools in lowlands, but locally occur to an altitude of 1,300 m (4,300 ft).

Like their relatives, the adult Laimosemion often inhabit very small isolated waters, but they are not annual species like some other killifish. The adults can move some distance over land to find another water source. They do this by repeatedly flipping their body. They commonly complete their life cycle in the water, often laying their eggs among plant material. However, their eggs can survive several days of drought, only hatching when again covered by water.

The largest are up to 8.5 cm (3.3 in) in total length, but most Laimosemion species only reach around half that size.

Until 2011, Laimosemion were included in Rivulus, and some prefer to maintain them in that genus.

If recognized as a valid genus, there are currently 35 species in Laimosemion: