A confined field assessment on the integrated control of vector mosquitoes (Culex tritaeniorhynchus and Anopheles sinensis) was conducted with larvivorous fishes (Aplocheilus latipes and Aphyocypris chinensis) and the timely treatment of Bacillus thuringiensis (H-14) formulation in marsh areas in Jindo Island, Chollanam-do from July through October in 1989. In presence of larvivorous fish (Aplocheilus latipes) at lower density of 0.8 fish per M$^2$ water surface, the natural control ranged 53.9-69.5% against Cx. tritaeniorhynchus from July to August, however, the encephalitis vector population increased over 10.0 larvae on the average per sample in late September, and B.t. (H-14) treatment at the rate of 1.0kg/ha made 100% vectors reduction in 24 hours, the control sustained above 90% until the test was terminated on October 12th. In the fish introduced rice paddies with Aphyocypris chinensis at the release rate of above 1. 5 fish per M$^2$, substantial degree of vector control was obtained in range of 60.8-77.0% against Anopheles and Culex combined, and the B.t. (H-14) treatment was made on September 28th which yielded a satisfactory degree of control maintained above 93.1% until October 12th. In marsh where the larvivorous fishes were absent, B.t. (H-14) treatments were made 3 times on August 12, 27 and September 28 to suppress vector mosquito population down.