Phenytoin follows Michaelis-Menten, a non-linear pharmacokinetics that occurs when drug molecules saturates the enzymes ability to metabolise the drug. When this occurs, steady state phenytoin serum concentration increases in a disproportionate manner after a dosage increase. General population data are usually used for the phenytoin dose calculation. However, many studies show that population pharmacokinetic parameters of phenytoin have high variations. Thus, use of specific local pharmacokinetic parameters for each population group in estimating individualised phenytoin dose can reduce phenytoin toxicity cases. This prospective, observational study was conducted to estimate a local Vmax and Km of phenytoin for adult epileptic patients in neurological ward and clinic at Hospital Pulau Pinang, Malaysia. All therapeutic drug monitoring of oral capsule phenytoin were studied in a three-month data collection period. Out of the 17 subjects in our study, there are 13 male subjects (76.47%) and 4 female subjects (23.53%). A total 11 Malay subjects (64.71%), 4 Chinese subjects (23.53%) and 2 Indian subjects (11.76%) were included. Median Vmax and Km were found to be 8.25 mg/kg/day and 3.80 mg/l. Male subjects have a higher Vmax (8.30 mg/kg/day) but a lower Km (3.3 mg/l). Chinese population has the highest Vmax (8.80 mg/kg/day). For Km, Indian population is the highest, with a value of 5.5 mg/l. From our study, gender does not correlate with Vmax and Km of phenytoin (p-value > 0.05). Ethnicity was also found to have no association with Vmax and Km (p-value > 0.05). Local Vmax (8.25 mg/kg/day) is higher and Km (3.8 mg/l) is lower when compared with standard Vmax (7 mg/kg/day) and Km (4 mg/l) obtained from Caucasian population.