Human embryonic stem cells (hESCs) represent a potential source of blood cells for transfusion therapies and a promising tool for studying the ontogeny of hematopoiesis. Moreover, human-induced pluripotent stem cells (hiPSCs), recently established by defined reprogramming factors expressed in somatic cells, represent a further source for the generation of hematopoietic cells. When undifferentiated hESCs or hiPSCs are cultured on either mesenchymal C3H10T1/2 cells or OP-9 stromal cells, they can be differentiated into a hematopoietic niche that concentrates hematopoietic progenitors, which we named "embryonic stem cell-derived sacs" (ES-sacs). We have optimized the in vitro culture condition for obtaining mature megakaryocytes derived from the hematopoietic progenitors within ES-sacs, which are then able to release platelets. These in vitro-generated platelets display integrin activation capability, indicating normal hemostatic function. This novel protocol thus provides a means of generating platelets from hESCs as well as hiPSCs, for the study of normal human thrombopoiesis and also thrombopoiesis in disease conditions using patient-specific hiPSCs.