Population changes of the mulberry tiger moth, Thanatarctia imparilis (Butler) (Lepidoptera: Arctiidae) and its carabid predator, Parena perforata (Bates) (Coleoptera: Carabidae) were surveyed at three disjunct study sites in the Kinki region, western Japan, from 1989 to 2001. At one of the three study sites, the population density of T. imparilis increased gradually, thereafter, decreased drastically, and then increased again. At this site, the number of P. perforata per prey colony changed closely with the density of T. imparilis. During the decline phase of T. imparilis, P. perforata was observed in over 80% of the prey colonies, and many egg masses of the beetle were deposited on each prey colony. It was observed that the effect of the predation acted strongly during the decline phase of T. imparilis. At another site, moreover, P. perforata was observed in over 80% of the prey colonies during the period of population decline of T. imparilis. At the third site of the three, however, the carabid beetles were observed in less than 10% of the prey colonies even during the decline phase of T. imparilis. At this site, the population density of T. imparilis decreased after high density had persisted for a few years and started to increase after low density had persisted for a few years. In addition, the change in amplitude between the highest density and the lowest density was ca. one-third that at the other two sites. It was suggested that the predator-prey interaction constitutes an important factor in explaining the different behaviors of T. imparilis populations at different localities.