Although many anuran species in Japanese paddy ecosystems are decreasing because of recent modernization of rice paddies, Fejervarya kawamurai is one of the exceptions, being extremely abundant even in modernized paddies. To understand the reason for this phenomenon, we collected specimens of anuran larvae in 92 paddy fields in west Mikawa area, Aichi Pref., Japan, and examined the biotic and abiotic factors affecting the density of F. kawamurai using model selection procedure with GLMM. The best model indicated that larval F. kawamurai tended to be abundant in paddies with low larval densities of Hyla japonica and Pelophylax nigromaculatus. Considering that F. kawamurai tends to start breeding later in the season than H. japonica and P. nigromaculatus, we hypothesize there are some negative effects of these preceding larvae on larval F. kawamurai. Such interspecific interactions are thought to have acted as an ecological constraint for F. kawamurai in the traditional Japanese paddy ecosystem, where many anuran species sympatrically breed. Recent decrease of some early breeders like P. nigromaculatus, however, would provide relief from such restrictions to F. kawamurai, and might promote the population increase and distribution expansion of this species.