Objective: To investigate the association between the CYP3A5 genetic polymorphism and the serum concentrations of carbamazepine (CBZ), to provide guidance for individualized drug dosing. Methods: Eighty-four epilepsy patients taking CBZ were included in this study. Their clinical data were recorded and CBZ serum concentrations were measured. The CYP3A5 6986 genetic polymorphism was assessed using a polymerase chain reaction-restriction fragment length polymorphism (PCRRFLP) assay. Patients were divided according to genotype into CYP3A5 expressor (CYP3A5*1/*1 genotype and CYP3A5*1/*3 genotypes) and non-expressor groups (CYP3A5*3/*3). The two groups were compared for the total dose of CBZ, dose of CBZ/kg body weight, serum drug concentration, dose-corrected serum concentration, and standardized serum concentration. Results: The total dose of CBZ and the dose of CBZ/kg body weight was higher in the CYP3A5 expressor group than the non-expressor (P = 0.043 and P = 0.014, respectively). The dose-corrected and standardized serum concentrations were lower in the CYP3A5 expressor group than the non-expressor (P = 0.001 and P < 0.001, respectively). There was however, no signifi cant difference in serum drug concentration between the two groups (P = 0.487). Conclusions: There was a close relationship between CYP3A5 genetic polymorphism and the serum concentrations of carbamazepine.