Objective: To investigate the effects of CYP2C9 and CYP2A6 genetic polymorphisms on plasma concentrations of sodium valproate （VPA） in the epileptic children． Methods: Epileptic children treated with sodium valproate only were collected in our study. Fluorescence polarization immunoassay was performed to measure plasma concentrations of sodium valproate. Direct sequencing and nest-PCR were applied to identify the genotypes of CYP2C9 and CYP2A6. One-way ANOVA was performed to analyze the influence of the polymorphisms on plasma concentrations of sodium valproate. Results: Patients were divided into 3 groups according to the genotypes of CYP2C9 and CYP2A6: extensive metabolizers （EM， CYP2C9*1*1 & CYP2A6*1*1）， intermediate metabolizers （IM， CYP2C9*1*3 & CYP2A6*1*1 or CYP2C9*1*1 & CYP2A6*1*4）， and poor metabolizers （PM， CYP2C9*1*3 & CYP2A6*1*4 or CYP2A6*4*4）， and the frequencies of the three groups were 73.5%， 24.1%， and 2.4%， respectively. The standardized blood drug concentration of IM was significantly higher than that of EM （P<0.05）. The mean of standardized blood drug concentration of PM was higher than the others， but there were no significant differences between them （P>0.05）. Conclusion: The plasma concentrations of sodium valproate can be affected by the polymorphisms of CYP2C9 and CYP2A6. Clinicians can choose appropriate initial dosage by detecting the genotypes.