Small scale field trials on control effect of three poison bait products against German cockroaches(Blattella germanica) were carried out in laboratory animal rooms and an apartment building in Seoul. The trial in the laboratory animal rooms showed that hydramethylnon 2% bait treatment gave the reduction rate of 96.6%, 99.2%, 99.0%, 99.5% and 97.8% in 2, 4, 8, 12 and 18 weeks after treatment respectively, and chlorpyrifos 0.6% bait treatment gave the reduction rate of 93.5%, 93.5%, 92.7%, 92.3% and 69.9% in 2, 4, 8, 12 and 18 weeks after treatment, respectively. The trial in the apartments showed that hydra-methylnon 2% bait treatment gave 81.4%, 88.8%, 91.5% and 95.6% of reduction rate on 2, 4, 6 and 8 weeks post-treatment respectively, chlorpyrifos 0.6% bait treatment gave 61.3%, 66.6%, 72.0% and 84.6% on 2, 4, 6 and 8 weeks post-treatment respectively, and fenitrothion MC 5% bait treatment gave 53.2%, 52.5%, 58.5% and 27.7% on 2, 4, 6 and 8 weeks post-treatment. Such differences in the reduction rate would be resulted from many factors, and the amount of the bait would be one of them, as shown that a package of the fenitrothion MC 5% bait and the chlorpyrifos 0.6% bait contained only 19.2g(3.2gx6discs) and 29g(2.9gx10discs) respectively whereas a package of the hydramethylnon 2% bait contained 66g(8.25gx8discs).