The pharmacokinetics of phenytoin was studied in 66 epileptic Chinese children and adults. The data were analysed by the population approach, using the non-linear mixed effect model, in the MULTI (ELS) program. There was no age or gender-related effect on either the apparent maximum elimination rate (k_max) or Michaelis-Menten constant (K_M). K_max was related to body weight 0.656. The population pharmacokinetics was similar in children and adults. K_max and K_M were estimated to be 30.72 mg·kg^–0.656 day^–1 and 2.307 mg·l^–1, respectively. K_max was higher than reported values, and K_M was comparable to that reported in a study in Japanese, but was much lower than that reported in studies of European patients. The inter-individual variability of K_M (CV 65.58%) was substantially higher than that of k_max (CV 28.49%), and the residual (intra-individual) variability was found 21.33% (CV).