To investigate the effects of Baicalein (BAI) on the proliferation and differentiation of pig preadipocytes, and elucidate its potential mechanism. Primary preadipocytes of pig were cultured in vitro. The morphologic changes of preadipocytes differentiation were observed by Oil Red O staining. Status of cell proliferation was detected by MTT assay. The degree of adipogenesis and differentiation were measured by Oil Red O staining extraction assay. The activity of fatty acid synthase (FAS) was detected by spectrophotometry. The mRNA expression of special peroxisome proliferation activated receptor-gamma2 gene (PPARgamma2) was detected by reverse transcriptase polymerase chain reaction (RT-PCR). When preadipocytes differentiated into adipocytes, the preadipocytes were changed from shuttle shape to oval or round, in which big and small lipid droplets were filled. The proliferation of preadipocytes was inhibited by the treatment of 160-640 micromol/L BAI (P < 0.05). The mRNA expression of PPARgamma2 and FAS activity and the differentiation of preadipocytes was repressed by 40-320 micromol/L BAI treatment (P < 0.05). It is concluded that the proliferation and differentiation of preadipocytes is inhibited by BAI in some degree. The effect of BAI on differentiation of preadipocytes may be resulted from inhibiting the mRNA expression of PPARgamma2 and reducing FAS activity.