To investigate the cell differentiation and the expression profiles of PPARy and C/EBPalpha mRNA, the rat preadipocytes were cultured after dispersed by enzymolysis of collagenase type I and the cell shape were observed under the microscope. The MTT method was adopted to determine the growth curve. The expression levels of PPARgamma and C/EBPalpha mRNA were also detected by relative quantitative RT-PCR. The growth of preadipocytes demonstrated an S-shaped or sigmoid curve. The PPARgamma mRNA in rat preadipocytes showed rather low transcript at day 3, but its expression level markedly increased by 2.5 fold at day 5 and remained at a higher level till day 9. Similarly, the expression level of C/EBPalpha mRNA in rat preadipocytes could hardly be detected at day 3 and dramatically increased at day 7. There was a 2.3 fold increase of C/EBPalpha mRNA expression level at day 7 compared with that at day 5. In a conclusion, this study suggested that both the initiating and maintaining of differentiation process were regulated by PPARgamma, while C/EBPalpha was likely to participate in the maintaining of differentiation process only.