We researched seasonal reproductive activity in the lesser Japanese mole, Mogera imaizumii, by morphometrical and histological methods for male internal genitalia using samples from Kanagawa Pref., central Honshu, Japan. On the basis of the weights of testis and the epididymis, we determined that their weights become higher during February–April. On the other hand, the histological profiles of seminiferous tubules showed variable states annually. In the late winter, a seminiferous tubule profile was mainly occupied with spermatocytes. In addition, in the spring, the profile was also occupied with spermatids increased in the profile. Moreover, from the early summer to the early winter, spermatogonia occupied and this status indicates lower reproductive activity. Accordingly, current results indicated that breeding behavior would be active during the late winter through spring in our research locality.