This study examined the effectiveness and repellency value of the commercial insecticide initial “KB” (Deltamethrin [0.6%]) to the German cockroaches. The research was performed by contact toxicity and repellent bioassay method using two populations; VCRU-WHO and RMKN-BKT. The effectiveness criteria are based on the value of knockdown time (KT) and lethal time (LT) that refers to the Directorate of Fertilizers and Pesticides of Indonesia, 2004. Results demonstrated that “KB” is effective in paralyzing the German cockroaches of VCRU-WHO (KT90 = 11.09 min) but ineffective in killing the population (LT90 = 43.65 h). This product is also ineffective either in paralyzing or killing the RMKN-BKT population (KT90 = 43.6 min, LT90 = 71.46 h). The repellency of “KB” is low in both populations and the resistant ratio value (RR50) revealed that RMKN-BKT has a low resistance to “KB”.