We assessed the responses of zooplankton communities with different population densities of an invertebrate predator, Mesocyclops pehpeiensis, to insecticide (carbaryl, 0.5 mgL(-1)) in small-scale mesocosm tanks (20 L). Cladocerans were eliminated by carbaryl application at both high and low predator densities. The density of rotifers increased after the elimination of the cladocerans by carbaryl application at low-predator density but not at high-predator density. Carbaryl application increased the relative importance of predatory interactions in the zooplankton community. The results suggest that predator abundance can affect the response of a zooplankton community to carbaryl application through predation on surviving zooplankton.