Abstract: In this experimental study, grass carp were bred in rice field (1.9 fish/m2) to control mosquito larvae. 78 days after treatment, the larvae population of An. sinensis and Cu. tritaeniorhynchus dropped down by 87.4% and 80% respectively. Newly hatched 1-2 instar larvae accounted for 73.3% of the larvae remained in rice field after treatment. Eighty-nine samples of fish feces taken from rice field and 10 fishes were examined for breathing sy-phons of mosquito larvae. Breathing syphons were found in 22 fecal samples (24.7% posi-live) and 3 fishes (30% positive). The average number of mosquito larvae devoured by one fish was 861.5 in 24 hours in tap water and 661 in 24 hours in water containing grass and aquatic plants. The simulated field test showed that the average number of mos-quito larvae devoured by fish was 362 larvae in 24 hours. The field trial indicated that the grass carp could not only cut down the mosquito larvae population but also benefit the peasants by increasing the production of both fish and rice.