Mesenchymal stem cell (MSC) has been known as a good source of progenitor for multiple connective tissue including cartilage, muscle, adipocyte, and bone. P-glycoproteins (P-gps) also known as ABCB1 that exports diverse substrates are the product of the multidrug resistance-1 (MDR-1) gene. P-gp expression has been reported in chondrosarcoma and hypertrophic chondrocyte in the human growth plate. This study was designed to investigate the expression of P-gp during chondrogenic differentiation of adult human stem cells. Bone marrow samples were obtained from nine human donors after informed consent. The isolated mononuclear cells (MNCs) were incubated as one pellet/tube and 0.5ml chondrogenic medium in the presence of 10ng/ml of TGF-beta 1 and TGF-beta 3 for 28 days. The expression of surface P-gps was analyzed by flow cytometry and quantitative RT-PCR was performed for the detection of mRNA expression of MDR-1 and type II collagen gene. Total collagen and glycosaminoglycan (GAG) contents of the pellets were measured. Surface P-gp expression of the MSCs was decreased during chondrogenic differentiation. MDR-1 gene was decreased 10-fold after the 2-week incubation whereas type II collagen gene was increased 491-fold after the 4-week incubation in chondrogenic medium. The total amount of collagen and GAG were increased during pellet culture. This study has demonstrated a decrease in expression of P-gp and down regulation of MDR-1 gene consistently by flow cytometry and quantitative RT-PCR, but an increased expression of type II collagen on MSC during chondrogenesis.