This study examined the differentiation character and pluripotency of mesenchymal stem cells (MSCs) under different conditions. Adult MSCs were initially isolated from the bone marrow of rats, cultured in vitro and identified by flow cytometry. After MSCs were transferred to osteogenic and adipogenic medium respectively, the morphological characterization of induced cells was observed. The expression of marker genes was detected by RT-PCR analysis. Then MSCs were transfected with lenti- viral vectors pGC-FU-Sox9-EGFP. Enhanced green fluorescence protein (EGFP) expression and trans- fection efficiency were determined by fluorescence microscopy. The results demonstrated that EGFP caused no effect on the multilineage potential of adult MSCs. Sox9 gene expression of high level was maintained stable in the transfected MSCs and induced MSCs to differentiate into chondrocytes. Ag- gracan was positive in chondrogenic lineages and the expression of aggracan and type Ⅱ collagenwas significantly increased during MSCs chondrogenic differentiation. It was concluded that Sox9 gene-modified adult MSCs may be promising candidate cells for further studies on tissue engineering. EGFP facilitates the research on MSCs physiological behavior and application in tissue engineering during differentiation both in vitro and in vivo. This study examined the differentiation character and pluripotency of mesenchymal stem cells (MSCs) under different conditions. Adult MSCs were initially isolated from the bone marrow of rats, cultured in vitro and identified by flow cytometry. After MSCs were transferred to osteogenic and adipogenic medium respectively , the morphological characterization of induced cells was observed. The expression of marker genes was detected by RT-PCR analysis. Then MSCs were transfected with lenti- viral vectors pGC-FU-Sox9- EGFP. Enhanced green fluorescence protein (EGFP) expression and trans - fection efficiency were determined by fluorescence microscopy. The results demonstrated that EGFP caused no effect on the multilineage potential of adult MSCs. Sox9 gene expression of high level was maintained in the transfected MSCs and induced MSCs to differentiate into chondrocytes. Ag- gracan was positive in chondrogenic lineages and the expression of aggracan and type II collagenwas significantl It was noted that Sox9 gene-modified adult MSCs may be so candidate cells for further studies on tissue engineering. EGFP facilitates the research on MSCs physiological behavior and application in tissue engineering during differentiation both in vitro and in vivo .