This　study　aimed　to　investigate　the　significance　of　cytokine　expression　in　supernatant　from　hematopoietic　stem/progenitor　cells　(HSCs/HPCs)　co-cultured　with　mesenchymal　stem　cells　(MSCs)　or　endothelial　progenitor　cells　(EPCs).　Mononuclear　cells　(MNCs)　were　isolated　from　normal　human　umbilical　cord　blood　and　then　cultured　solely　or　co-cultured　with　MSCs　or　EPCs.　Changes　in　the　number　of　MNCs　and　HSCs/HPCs　were　observed,　and　MNC　proliferation　was　tested　by　carboxyfluorescein　diacetate　succinimidyl　ester.　The　cultured　supernatants　of　the　treated　MSCs　and　EPCs　were　collected　at　24　h　after　co-culture　and　used　to　determine　the　concentrations　of　IL-3,　IL-6,　stem　cell　factor　(SCF),　TPO,　Flt3l,　and　VEGF.　The　total　number　and　proliferation　of　MNCs　increased　significantly　when　co-cultured　with　MSCs　or　EPCs　than　when　cultured　alone,　particularly　when　MNCs　were　co-cultured　with　EPCs.　The　differences　in　IL-3　and　Flt3l　concentrations　between　groups　were　not　significant.　However,　IL-6　in　the　MSC　group　was　significantly　higher　than　that　in　the　two　other　groups.　The　SCF　and　TPO　concentrations　were　highly　expressed　in　the　EPC　group.　The　VEGF　concentrations　in　the　MSC　group　and　the　EPC　group　were　higher　than　those　in　the　control　group.　These　results　indicated　that　MSCs　and　EPCs　possibly　favor　the　proliferation　of　MNCs　and　HSCs/HPCs.　IL-6　and　VEGF　may　be　related　to　hematopoietic　reconstitution　and　homing　ability　of　HSCs/HPCs.　TPO　may　have　a　specific　relationship　with　the　promotion　of　HSCs/HPCs　differentiation.