To study the effect of GM-CSF on in vitro expansion of megakaryocyte progenitor cells from cord blood, CD34(+) cells isolated by magnetic cell sorting system (MACS) were cultured in serum-free medium containing TPO, IL-3, SCF and with or without various concentrations of GM-CSF (5, 20, 100 ng/ml). The numbers of MNC, proportion of CD34(+)CD41(+) cells and CFU-MK were measured at 6, 10 and 14 days. The results showed that the expansion of MNC and proportion of CD41(+) cells was accelerated distinctly by various concentrations of GM-CSF after 14 days, while 20 and 100 ng/ml GM-CSF exhibited higher expansion effect than that of 5 ng/ml. TPO + IL-3 + SCF with 5 ng/ml or 20 ng/ml GM-CSF could stimulate the formation of CFU-MK, while TPO + IL-3 + SCF with 100 ng/ml GM-CSF could inhibit it. It is concluded that GM-CSF can accelerate the expansion of megakaryocyte progenitor cells from CD34(+) cells in cord blood in the serum-free medium containing TPO + IL-3 + SCF.