This invention provides a method for preparing dendritic cells from monocytes with the use of interferon α via non-adhesive culture. The method for preparing cytotoxic dendritic cells from monocytes comprises subjecting monocytes which were isolated from the peripheral blood to non-adhesive culture in the presence of GM-CSF and pegylated interferon α, and further conducting non-adhesive culture with the addition of prostaglandin E2 and OK432.