Objective To preliminarily explore the resistance mechanism of pyriproxyfen-resistant Culex pipiens pallens by comparing the biochemical characteristics of glutathione s-transferases (GSTs) between resistant and susceptible populations of Cx. pipiens pallens. Methods The pyriproxyfen-resistant and susceptible populations of Cx. pipiens pallens were chosen through indoor successive selection as the research objects. And the activities of GSTs were determined according to the method reported by Habig et al. (1976). Statistical analysis was thus performed using the t-test for sample mean comparison. Results The optimal substrate of GSTs from Cx. pipiens pallens was 1-chloro-2, 4-dinitrobenzene (CDNB). When CDNB was used as the substrate, the activities of GSTs in the resistant and susceptible populations were 3.626×10^-4 and 2.737×10^-4 nmol/mg protein·min, respectively. The hydrolytic activity of Cx. pipiens pallens GSTs increased with the elevation of substrate concentrations[i.e., CDNB and DCNB (1, 2-dichloro-4-nitrobenzene)]. In a certain concentration range, the hydrolytic activity of GSTs in the resistant population was slightly higher than that in the susceptible population towards both substrates. When CDNB was used as the substrate, the Michaelis constant (Km) and maximum reaction rate (Vmax) of GSTs in the resistant population were 8.01 mmol/L and 4.87×10² μmol/min·mg, respectively, while those in the susceptible population were 1.11 mmol/L and 3.87×10² μmol/min·mg, respectively. There were significant differences between these two populations regarding Km and Vmax (t_a=11.415, t_b=6.411, all P<0.05). When DCNB was used as the substrate, there was no significant difference between the two populations regarding Km and Vmax of GSTs (t_c=0.134, t_d=1.280, all P>0.05). Conclusion GSTs may play an antidotal and metabolic role in the formation of pyriproxyfen resistance in Cx. pipiens pallens.