The chromosome numbers and karyotypes of two species of Halophila are reported. Somatic chromosome numbers of the two species all were 2n=18(x=9). Their karyotype formulas were as follows: 2n = 2x = 18 = 4m + 14sm for H. ovalis (R. Br.) Hook. f., and 2n = 2x = 18 = 8m + 10sm for H. beccarii Asch which is reported for the first time. The karyotypes of the two species belong to category 2B of Stebbins.