The diet of two rice-field inhabiting snakes, Elaphe quadrivirgata and Rhabdophis tigrinus, was examined with reference to rice-field anuran fauna. Although adult Hyla japonica and Rhacophorus schlegelii inhabit rice fields temporarily in spring for reproduction, juvenile Rana nigromaculata and Rana limnocharis are residents of rice fields after emerging in early summer. In response to these seasonal changes, both snakes shifted their prey selection dramatically from adults of H. japonica and Rh. schlegelii in spring to juveniles of Ra. nigromaculata and Ra. limnocharis in summer. These results strongly suggest that the seasonal partitioning of rice-field habitats between small adult frogs and juveniles of larger frogs allows these snakes to continuously forage in rice fields throughout the warm season.