Several local populations of the moor frog (Rana arvalis) from the southern part of the range (the Ukraine) were compared by size and age composition and morphological characters in males and females with one of the populations from Moscow Region (Zvenigorod Biological Station-ZBS). In spite of close geographical location of the Ukrainian populations (not more than 40 km), they differ significantly both in mean body size and age. At that, mean value of these parameters turned out to be lower than the corresponding values for the ZBS population. In southern populations, the proportion of females breeding for the first time right after the second hibernation is higher than males; comparing to the ZBS population, the part of two-years-old mature specimens of both sexes is higher while the part of older specimens is lower. This geographical variability of age composition causes significantly lower mean age and body size of specimens from the southern populations. Although in the Ukraine the activity season is longer than in Moscow Region, the growth rate of two- and three-year-old frogs from southern populations is lower, and only at age of four they become larger than specimens from the ZBS population. These differences are caused by higher reproductive effort both in females and males from southern populations. Morphologically, males and females from southern populations differ most significantly by shin and hip length (absolute and relative values of the characters are higher in males). As compared to the Ukrainian populations, both sexes in the ZBS population have lower values of these characters. The overall sex differences by absolute and relative values of these characters are more pronounced in the ZBS population. Meanwhile, concerning body size, males are bigger than females in the ZBS population, and this difference remains and is even more pronounced in the southern populations. Geographic variation in body size is more expressed in females than in males, which corresponds to more significant sex differences in the Ukrainian populations in this regard. The reason behind this lies in dissimilarity in reproductive strategies: males from the ZBS population participate in the breeding for the first time at younger age than females whereas in the Ukrainian populations males take part in reproduction at older age (hence, at bigger size) which ensures their greater reproductive success.