Abstract:The present paper deals with astudy of the karyotype analysis of two species of Alismataceae——i>Alisma orientale(Sam.)Juzepcz and Sagittaria sagittifolia L., The photomicrographs of the chromosome complements and idiograms are given in Fig. 1 and Fig. 2. Paramerers chromosomes are given in Table 1. According to terminology defined by Levan et al. [10], the karyotype formula of Alisma orientale is K(2n)=14=10m+2t(SAT)+2t and that of Sagittaria sagittifolia is K(2n)= 22 = 2m + 2sm + 10st + 8t. The complements are 2n=14=2L=6M2+2M1+4S and 2n=22=2L+6M2+12M1+2S respectively according to Kuo et al.Comparing the karyotype of Alisma orientale with that of Sagittaria sagittifolia shows that the latter belongs to "3B" type of Stebbins‘s karyotypic classification and should therefore be considered as one more advanced than the former which belongs to "2B". According to the cytological data provided by Sharma et al. and the author, it seems that Sagittaria is also more advanced than Alisma. These conclusions are supported by morphology and palynology.