Effects of photoperiod on nymphal development were investigated in two subtropical populations of Periplaneta japanna living on Naha, Okinawa Islands (26 N) and Hachijo island (N33 N), Japan. Nymphal development was greatly influenced by photoperiod with different photoperiodic response pattern occurring between Okinawa and Hachijo population. In the Okinawa population, nymphs developed faster under LD 16:8h and LD 14∶10h than under LD 12∶12h at constant photoperiods. When photoperiodic shifts from long days (LD 16∶8h) to short days (LD 12∶12h) at 60 and 120 days restrain nymphal development, while photoperiodic shifts from short days to long days accelerate the nymphal development. However in Hachijo population, nymphal development was the fastest under LD 12∶12h, followed by LD 14∶10h and the slowest under LD 16∶8h. Nymphal growth is restrained when the nymphs are transferred from LD 16∶8h to LD 12∶12h at 60 and 120 days after hatching, rapid development is observed when nymphs were transferred in the opposite direction in Hachijo population. The different photoperiodic response pattern in nymphal development between the two parapatric geographical populations might be regarded as the result of divergent evolution.