The relationship between the population dynamics of ricefield rats Rattus argentiventer and their food supply, rice plants, was investigated in an enclosure in Jatisari, West Java. The density of the rat population fluctuated greatly throughout the year depending on the growth stages of the rice plants. A model illustrating the responses of the rat population to the growth stages of the rice plants is described. The population increased following periods when high-quality rice plants were available, and decreased following periods when only low-quality rice plants were available. The highest rate of increase (r) over a 2-week period was observed during the dry season of 1989 (r=1.77). The lowest rate of increase over 2 weeks was observed during the rainy season of 1989–90 (r=−0.59). The maximum rate of increase for the ricefield rat in the numerical response function was 1.183 month−1, and the best estimate for the numerical response function was robs=−3.890+5.043(1−e−0.026V).