Abstract: Aster ser.Hersileoides Ling(Aster,Asteraceae) endemic to western China consists of only two geographically restricted species,Aster hersileoides Schneid and Aster nitidus Chang.The mitotic chromosome numbers and the karyotypes of the two species were investigated for the first time.The results showed that both species were diploids with small chromosomes ranging from 1.64μm to 2.8μm and that their karyotypes were formulated as 2n=2x=18=16m+2sm,belonging to 1A type.