Using skeletochronology, we compared age structure in the breeding season in two populations (Katata, Shiga Pref. and Shizuhara, Kyoto Pref.) of a pond frog, Rana nigromaculata from central Japan and elucidated interpopulation variation in some life history traits. Newly metamorphosed froglets were larger in SVL, heavier in body mass, and fattier in Katata than in Shizuhara. In both populations, the age at first reproduction was 2 yrs for males and 3 yrs for females. Longevity was estimated to be at least 5 and 6 yrs at Katata and Shizuhara, respectively, for both sexes. Females were on an average significantly older than males in both populations. The modal age in breeding males was 2 yrs in Katata but 4 yrs in Shizuhara, and Katata males (mean=3.27 yr) tended to be younger than Shizuhara males (mean=3.42 yr), although the difference was not significant. Similarly, females did not differ in the mean age in the two populations (4.1 yrs in both populations). In SVL, females were significantly larger than males in both populations. In males, SVL was larger in Shizuhara than in Katata, but females did not differ in SVL. Shizuhara males grew faster than Katata males, but females did not differ in growth rate in both populations. Interpopulation differences in age and size properties of R. nigromaculata seem to be related to degree of interspecific competition and food consumption. We briefly discussed use of skeletochronology in relation to amphibian declining problems.