The purpose of this investigation was to determine pharmacokinetic parameters of gentamicin using nonlinear least square regression(NLSR) and Bayesian analysis in Korean normal volunteers and gastrointestinal surgical patients. Nonparametric expected maximum(NPEM) method for population pharmacokinetic parameters was used. Gentamicin was administered every 8 hours for 3 days by infusion over 30 minutes. The volume of distribution(V) and elimination rate constant(K) of gentamicin were $0.226{pm}0.032,;0.231{pm}0.063L/Kg;and;0.357{pm}0.024,;0.337{pm}0.041hr^{-1}$ for normal volunteers and gastrointestinal surgical patients using NLSR analysis. Population pharmacokinetic parameters, KS and VS were $0.00344{pm}0.00049(hr{cdot}ml/min/1.73m^2)^{-1};and;0.214{pm}0.0502L/Kg$ for gastrointestinal surgical patients using NPEM method. The V and K were $0.216{pm}0.048L/Kg;and;0.336{pm}0.043hr^{-1}$ for gastrointestinal surgical patients using Bayesian analysis. There were no differences in gentamicin pharmacokinetics between NLSR and Bayesian analysis in gastrointestinal surgical patient.