Studies showed that co-transplantation of mesenchymal stem cells (MSCs) and cord blood-derived CD34+hematopoietic stem cells (HSCs) offered greater therapeutic effects but little is known regarding the effects of human Wharton's jelly derived MSCs on HSC expansion and red blood cell (RBC) generation in vitro. This study aimed to investigate the effects of MSCs on HSC expansion and differentiation. HSCs were co-cultured with MSCs or with 10% MSCs-derived conditioned medium, with HSCs cultured under standard medium served as a control. Cell expansion rates, number of mononuclear cell post-expansion and number of enucleated cells post-differentiation were evaluated. HSCs showed superior proliferation in the presence of MSC with mean expansion rate of 3.5 × 108 ± 1.8 × 107after day 7 compared to the conditioned medium and the control group (8.9 × 107 ± 1.1 × 108and 7.0 × 107 ± 3.3 × 106respectively, P