Three populations in Caltha palustris and five in C. scaposa from China, two closely related species in the small genus Caltha of the Ranunculaceae, have been cytologically investigated. Of the populations checked in C. palustris, the Nayong population from Guizhou has the chromosome number of 2n=32 (tetraploid), and the two Zhongdian populations from Yunnan have the number of 2n=64 (octoploid). Among those checked in C. scaposa, the Hongyuan, Kangding, and Serxu populations from Sichuan all have the tetraploid number of 2n=32, and the Nyingchi population from Xizang and the Deqen population from Yunnan both have the octoploid number of 2n=64. We have performed a karyotypic analysis on most of these populations. The present results, together with those reported previously, show that both C. palustris and C. scaposa from China may have undergone strong differentiation among populations in ploidy level and karyotypic constitution. Caltha palustris from China includes at least three cytotypes with different ploidy levels, namely, the tetraploid cytotype with 2n=32, the hexaploid cytotype with 2n=48, and the octoploid cytotype with 2n=64. The tetraploid cytotype is the commonest and the most widespread, and currently only in northwestern Yunnan all the three cytotypes have been found to co-occur. Caltha scaposa from China includes two cytotypes, the tetraploid cytotype with 2n=32 and the octoploid cytotype with 2n=64, with the former occurring in the northeastern part of the geographical range of the species while the latter in the southwestern part. Although the 32 or 64 chromosomes in both C. palustris and C. scaposa can be roughly arranged into eight groups of four or eight homologues, in some of the groups there often exists obvious heteromorphy among the presumably homologous chromosomes, and thus different populations are more or less distinct in karyotypic constitution. Although C. palustris and C. scaposa are the two most closely related species in the genus, they are revealed to be rather well differentiated chromosomally, particularly in chromosome size. The chromosomes in C. scaposa are smaller than those in C. palustris, which may represent a derived condition.