Th e paper first describes in detail the karyotype of Pelobates vespertinus (Pallas, 1771) in comparison with the karyotype of Pelobates fuscus (Laurenti, 1768). Comparative morphological analysis of chromosomes has shown that these two cryptic species have a symmetrical karyotype consisting of two-armed chromosomes. It has been established that their chromosome sets consist of 7 pairs of large chromosomes and 6 pairs of small ones. The species diff er by the position of the centromere in the chromosomes of the 10th and 11th pairs. Th e 10th pair of P. fuscus is metacentrics, the 11th pair is submetacentric; the 10th pair of P. vespertinus is submetacentric, and the 11th one is metacentrics. Secondary constrictions are on the short arms of the 7th chromosome pair. The chromosomal formula for both species is 4 meta-(m) + 7 submeta-(sm) + 2 subtelocentrics (st), 2n = 26, N.F. = 52. Absolute length of all the chromosomes in the karyotype of P. fuscus is somewhat larger than that one in the karyotype of P. vespertinus. The parameters of relative length are equivalent on average, but they differ in individual chromosomes. On the background of established chromosomal differences between the cryptic species, reliable diagnostic features have not been identifi ed.