AbstractCarbonic anhydrases (CAs) are metabolic enzymes that regulate the physiological equilibrium in a variety of organisms. In this study, we investigated the function of CA II in Culex pipiens pallens using real‐time quantitative polymerase chain reaction and double‐stranded RNA injection. CA II transcripts were more abundant in the deltamethrin‐susceptible strain than the deltamethrin‐resistant strain. The activities of metabolic enzymes increased when the CA II expression was silenced. These findings suggest CA II regulates deltamethrin resistance by altering metabolic enzyme activity, and could serve as a potential genetic marker for monitoring deltamethrin resistance in mosquitoes.