A confined field release of the potential larvivorous native fish, Aphyecypris chinensis** in natural rice paddies and stream seerage was conducted in 1979 and 1981. The fish were released at the rate of 1.5 to 1-pair in rice paddies of Wondang-Ni, Kyunggi Province and 1-pair per 1-M$^2$ water surface in stream seepage of Nokbon-Dong, outskirt of Seoul. Fish stocking of 1.5 per 1-M$^2$ in Wondang-Ni rice paddy resulted in mosquito larva: reduction of 44.4 ％, 84.3％ and 98.9％ in 1,2 and 3 week periods against 4 species combined, Anopheles sinensis, Culex pipiens, C. orientalis and C. tritreniorhynchus and thereafter, no mosquito larvae were sampled from the plot showing satisfactory degree of control. Fish stocking of 1-pair per 1-M$^2$ water surface in rice paddy resulted in the similar pattern of mosquito reduction with the satisfactory level of sup pression reached one week earlier; over 90％ mosquito reduction was marked in second week after the fish introduction. In stream seepage, fish release at the rate of 1 pair oner 1-M$^2$ wafer surface produced over 90％ mosquito larval reduction in one week and thereafter, continuous mosquito suppression had been maintained until the experiment was terminated on October 27th. An overall reduction based on sample data in this experiment was 94.0％. Our release experiment suggests that the fish, Aphyocypris chinensis should be considered highly promising for further larger scale release trials against vector mosquito larvae particularly breeding in rice paddies in South Korea at the release rate of 1 to 1.5 fish per 1-M$^2$ water surface.