Background : Prednisotone(PDL) and prednisone(PDN) exhibit nonlinear, dose-dependent pharmacokinetic characteristics affected by the administered dose. We estimated the pharmaco-kinetic parameters of PDL and PDN after high dose(Img/kg) administration of PDL or PDN orally or intravenously. We also assessed the relative bioavailability of PDL and PDN powder which are administered orally as a capsule. Method : Img/kg doses of iv PDL, oral PDL and oral PDN were administered to 8 male healthy volunteers in a randomized three-way crossover design. Blood samples were drawn serially upto 12 hours and we also collected urine during that time. Plasma and urine concentrations of PDL and PDN were measured by high performance liquid chromatography. Pharmaco-kinetic parameters were estimated by compartmental or non-comparoental model. Results : Whether we administered PDL or PDN, the major compound found in plasma was PDL, and the concentration-time curves of PDL and PDN showed parallel decay with concentration ratio 4 to 10 throughout the elimination phase. Total clearance($Cl_T$) and volume of distribution(Vdss) of PDL were estimated to 3.28${pm}$0.42m1/min/kg and 0.68${pm}$0.12Lf/kg and the $clearances(Cl_{oral})$ of PDL and PDN after erat dose were 5.21 ${pm}$ 0.48ml/min/kg and 52.0${pm}$13.1 ml/min/kg respectively. After dministration of PDL or PDN,8.20-14.5% of the dose adminis-tered excreted renally as a PDL form and 1.14-1.54% of dose as a PDN form. Relative bioavailability of PDL and PDN powder were estimated to 64.4${pm}$ 6.5% and 55.8${pm}$ 7.1% , respectively. Conclusion : Pharrnacokinetic properties of PDL and PDN seems to be affscted largely by the administered dose rather than by the route of administration or drug form, and mean relative bioavailability of PDL and PDN powder were 64.4% and 55.8%, respectively.