The author carried out a study on the effectiveness of the boric acid as a stomach poison for German cockroach control from July to September 1971. The test was performed by the feeding method under conditions of 20 degrees C and 80 per cent relative humidity. The baits were composed of one control group and five different combination groups with boric acid and sugar as follows. 1)10 g sugar only(control group), 2)1 g powedered boric acid to 9 g sugar(1:9 poison baits), 3)2 g powdered boric acid to 8 g sugar(2:8 poison baits), 4)4 g powdered boric acid to 6 g sugar(4:6 poison baits), 5)5 g powdered boric acid to 5g sugar(5:5 poison baits), 6)10 g powdered boric acid only (10:0 poison baits). The insects were composed of 360 female adult German cockroaches collected by traps at the kitchens of restaurants and house holds in Seoul City. The results were as follows: 1.The total mortality by poison baits in 72 hours after treatment were: 1)44.3 % by 1:9 poison baits, 2)79.4 % by 2: poison baits, 3)96.7 % by 4:6 poison baits(the most effective poison baits), 4)88.3 % by 5:5 poison baits, 5)91.1 % by 10:0 poison baits. 2.The peak mortality by the treatment hours were: 1)Up to 21 hours: 23.3 % by 5:5 poison baits, 20.0 % by 10:10 poison baits, 2)From 24 to 48 hours: 71.1 % by 4:6 poison baits, 55.6 % by 10:0 poison baits, 3)From 48 to 72 hours: 21.9 % by 2:8 poison baits, 19.6 % by 1:9 poison baits. The most effective treatment hours was from 24 to 48 hours.