Abstract: To investigate the effects of protein kinase C (PKC) on proliferation, extracelluar matrix synthesis and transcriptional factor SOX9 (SRY-related high mobility group-box gene 9) expression of rat growth plate chondrocytes in vitro. Rat costochondral growth plate chondrocytes (RGC) were isolated and cultured. The 1st serum free cultured passage RGCs were treated with 1, 10 and 100nmol/L phorbol 12,13-dibutyrate (PDBu), PKC agonist, cell morphology alterations were observed with inverted microscopy, cell proliferation, COLLAGEN and GAG synthesis were detected by isotope incorporation COLLAGEN TYPEⅡ and AGGRECAN mRNA transcription and SOX9 expression were revealed by RT-PCR and Western blot. 100nmol/L PDBu treatment made the cell morphology of serum free cultured RGC closed to serum group and inhibited proliferation but promoted COLLAGEN and AGGRECAN synthesis, 3H-TdR、3H-proline and 35S-sulfate incorporation of 100nmol/L PDBu group were as 83%, 52.6% and 146.5% as those of serum free control（P<0.05）. COL2A1 ， AGGRECAN gene transcription and SOX9 expression were also enhanced by 100nmol/L PDBu treatment. There were no obvious effects of 1nmol/L and 10nmol/L PDBu on 1st RGC. Our results indicate that activated PKC inhibits growth plate chondrocyte proliferation and promotes differentiation.