Abstract: Hybridization experiments were conducted by forced mating between Anopheles minimus from Guangxi (G) and Yunnan (Y).F1 hybrid females were all fertile with normally developed ovaries.(Y×G) F1 males were all sterile,with abnormally enlarged testes.(G×Y) F1 males,though fertile,showed somewhat atrophic testes,and when they were back crossed with parental females,the latter produced eggs with very low hatching rate.Ovarian nurse cell polytene chromosomes from F1 hybrid females showed partial asynapsis in X chromosome as well as in autosonles,asynapsis at 38 zone in 3L being the most constant.It was obvious that there was definite,though partial,reproductive isolation between An minimus from Guangxi and that from Yunnan.Whether they are sibling species remains to be further investigated (Figs.1-8).