Abstract:The semi-wild races of Gossypium hirsutum are indigenous to Mexico. It becomes one of the important germplasms in the breeding of Upland cotton, but the cytogenetical study is still lacking. In this paper, the karyotypes of 8 semi-wild races were analyzed. The chromosome number of root tip cells in all races was 52. The “race mexicanum”, “race latifolium”, “race parmeri” and “race panctatum” belong to 1 B karyotype. Among them, the “race mexicanum” is the most primitive one, 2n=4x=52=44m (6SAT)+8sm. The races with 2 B karyotype were “race yucatanense”, “race marie-galante”, “race morilli” and “race richmondii”, the last two races were more advanced, 2n = 4x = 52 = 32 m (2 or 4 SAT) +20sm. According to the results of karyotype analysis, the possible relationship in evolution of races is discussed.