The glycogen branching enzyme (GBE) gene has been cloned from Culex pipiens pallens. An open reading frame of 2,070 bp was found to encode a putative 689 amino acid protein. The deduced amino acid sequence shares 82% and 60% identity with GBE genes from Aedes aegypti and Homo sapiens. Transcript expression of GBE was determined by real-time polymerase chain reaction in deltamethrin-susceptible and deltamethrin-resistant strains of the Culex mosquito. The results demonstrated that this gene has 19.7-fold higher expression in deltamethrin-resistant strain. Unexpectedly, the following study showed that cell proliferation decreased obviously in the GBE overexpression group compared to the empty vector control or the unrelated gene when treated by deltamethrin in the mosquito C6/36 cells whose mechanism is still unexplained. Our study provides the first direct evidence that GBE gene may play some role in the development of deltamethrin resistance in C. pipiens pallens.