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 (kmax) or Michaelis-Menten constant (KM). Kmax was related to body weight 0.656. The population pharmacokinetics was similar in children and adults. Kmax and KM were estimated to be 30.72 mg.kg-0.656 day-1 and 2.307 mg.l-1, respectively. Kmax was higher than reported values, and KM 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 KM (CV 65.58%) was substantially higher than that of kmax (CV 28.49%), and the residual (intra-individual) variability was found 21.33% (CV).