An object of the present invention is to provide a method of promoting polyploidization of megakaryocytes and thereby producing highly polyploidized megakaryocytes, a method of efficiently producing platelets from polyploidized megakaryocytes, and the like. The present invention provides a method of producing polyploidized megakaryocytes comprising a step of forcing expression of an apoptosis suppressor gene in megakaryocytes before polyploidization and culturing the resulting cells.