We examined cytogenetic features and reproductive capacity in newly arisen tetraploid amphibians. Autotetraploids were produced by suppressing second polar body formation in haploid eggs of diploid females of Rana nigromaculata inseminated with diploid sperm of autotetraploid R. nigromaculata. Allotetraploids were also produced by suppressing second polar body formation in haploid eggs of diploid females of Rana porosa brevipoda inseminated with diploid sperm of autotetraploid R. nigromaculata. In male R. nigromaculata autotetraploid offspring, mostly quadri- and bivalents were found in Metaphase I, and 26 dyads were seen in Metaphase II. Autotetraploid males were then mated with autotetraploid females, and most of the resultant offspring were tetraploids possessing four chromosome sets of diploid R. nigromaculata. Male allotetraploid offspring showed 26 bivalents in Metaphase I and 26 dyads in Metaphase II. A large number of the offspring resulting from crosses between allotetraploid males and females were tetraploids having chromosome sets of diploid R. nigromaculata and diploid R. p. brevipoda. These results seem to indicate that, if such tetraploids develop a distinguishing premating mechanism, they should continue as a sexual fertile species in one generation and coexist with their diploid parental species.