Oviposition and overwintering ability of Japanese cockroach, Periplaneta japonica Karny, captured in Sapporo in early summer (June and July) of 2012 were examined under room conditions without heating. The numbers of egg cases laid monthly and their hatching rates were the highest, in August during the observation period. High survival rates after overwintering were observed in the second to the fourth instars of nymphs, whereas survival rates of the first instar were relatively low.