The rice leaf bug, Trigonotylus caelestialium (Kirkaldy), is a major species of stink bugs causing pecky rice. Seasonal prevalence of occurrence of this bug on rice plants in paddy fields was investigated by a sweeping method in Niigata Prefecture. The number of adult bugs captured by sweeping increased just after the rice plants reached the heading time, however it decreased quickly thereafter. The density of adults tended to be higher in an extremely early variety and an early variety of rice plant than a medium one. The number of males was more than the number of females, and the numbers fluctuated heavily. The nymphs appeared mainly from the middle to the end of the grain filling period. These nymphs originated from eggs laid by females which invaded the rice plants at the time of heading. The percentage of pecky rice grains tended to be high in the extremely early variety which showed a high hull-cracked rice rate. Most of the pecky rice grains were damaged at the top or suture of the grains. Hull-cracked rice began to appear 10 days after heading time and increased to the maturing stage. Pecky rice grains began to appear 15 days after the heading time. Damage at the top part of the grains did not increase after maturation. On the other hand, grains damaged at the suture increased markedly up to maturing stage.