© 2022, African Association of Insect Scientists.German cockroach (Blattella germanica L. Blattodea: Ectobiidae), a common species in the genus Blattella, is known as a mechanical vector of many pathogens and parasites. Different classes of insecticides are used with synergistic substances to treat cockroach infestations. In this research, we examined the synergistic effect of piperonyl butoxide (PBO) on the toxicity of two pyrethroids (alpha-cypermethrin and deltamethrin) which are insecticides recommended for in-home cockroach control, against four pyrethroid-resistant strains of B. germanica from Turkey. Cockroaches were exposed to both pyrethroids and their combinations with PBO (insecticide: synergistic ratio is 1:0.5). The results show that the PBO has a synergistic effect on the pyrethroid insecticides and the exposure of German cockroaches to PBO significantly suppressed (p ≤ 0.05) resistance to both insecticides.