OBJECTIVE To investigate the effect of human platelet lysates (HPL) obtained from platelet-rich plasma on the proliferation and biological characteristics of human mesenchymal stem cells (MSCs) in vitro. METHODS HPL was obtained by repeated freeze-thawing of human plateletes, and the MSCs separated by density gradient centrifugation from 6 donors were expanded in medium supplemented with 10% fetal bovine serum (FCS) or HPL at different concentrations. The optimal concentration of HPL for cells culture was determined according to the cell proliferation kinetics. The cultured MSCs were characterized for their proliferation, cell phenotype, and cell cycle distribution. RESULTS The HPL-supplemented medium contained 4 essential growth factors for the growth of MSCs, namely platelet-derived growth factors (0.53∓0.06 ng/ml), basic fibroblast growth factor (37.5∓4.31 pg/ml), insulin-like growth factor-1 (0.15∓0.06 mg/ml) and transforming growth factor (5150∓463 pg/ml). Cultured in the presence of HPL at the optimal concentration of 7.5%, the MSCs displayed a spindle-shaped fibroblast-like morphology without obvious changes in the proliferation activity till passage 8 (P>0.05), similar to those of cells in FCS-supplemented culture medium. Flow cytometry and cell cycle analysis revealed no differences in the phenotypes or cell cycle distribution between the cells cultured in the presence of 7.5% HPL and 10% FCS. CONCLUSIONS The culture medium supplemented by 7.5% HPL can promote the expansion of human MSCs and maintain the basic biological characteristics of the cells.