The microsomal CYP2C9 alleles involved in the biotransformation of propofol, a widely used anesthetic agent, were investigated in vitro. To examine the enzymatic activity of the CYP2C9 alleles, kinetic parameters for propofol 4-hydroxylation were determined in recombinant human P450s CYP2C9 microsomes from Sf21 insects cells carrying CYP2C9*1 and other variants. Some of the variants showed decreased enzyme activity compared with the wild type, as previously reported. Two variants (CYP2C9*36 and *56) were found substantially to increase intrinsic clearance relative to the wild type variant. Most variants significantly (p<0.05) decreased intrinsic clearance of propofol compared with the wild type, except *11, *47, and *54. This study is the first to report these rare alleles for propofol metabolism, providing fundamental data for further clinical studies on CYP2C9 alleles for propofol metabolism in vivo.