BACKGROUND: Pilose antler polypeptides (PAP) have been proved to promote the proliferation of condrocytes cultured in vitro and expressions of glycosaminoglycan (GAG), type Ⅱ collagen and Aggrecan protein in the extracellular matrix.OBJECTIVE: To investigate the feasibility of chondrogenic phenotype differentiation of rabbit bone marrow-derived mensenchymal stem cells (BMSCs) in a defined medium and then to study the effect of PAP on chondrogenic differentiation of BMSCs in vitro.METHODS: The third passage BMSCs from rabbits were randomly divided into control group cultured in ordinary medium, induced group cultured in defined medium, and PAP group cultured in defined medium containing 10 mg/L PAP. An equal volume of articular chondrocytes were selected from rabbits as articular cartilage group. The cellular morphological and functional characteristics were observed after 1, 2, 3 weeks in centrifuge tubes by histological, biochemical and reverse transcription-polymerase chain reaction (RT-PCR) technique. RESULTS AND CONCLUSION: Cell masses in the control group gradually crumbled after 2 weeks, and hematoxylin-eosin staining could not be done. Cell masses in the induced and PAP groups were semitransparent, but slightly contracted. A part of these cells were round or oval with a high density distribution at the surface. The content of GAG and mRNA expression of type Ⅱ collagen in the induced and PAP groups were increased with culture time, and higher than those in the control group at different time points (P < 0.05). The content of GAG and mRNA expression of type Ⅱ collagen in the PAP group were higher than those in the induced group, but lower than those in the articular cartilage group (P < 0.05). The results indicated that BMSCs can differentiate into chondrogenic phenotype in the defined medium, and PAP can significantly enhance chondrogenic phenotype differentiation of BMSCs. But the quality of cultured cartilage tissue is poorer than that of the articular cartilage.