An object of the invention is to provide a method of producing a pharmaceutical composition that contains cat or feline erythropoietin (fEPO) as the active ingredient and has, when administered in humans and/or animals, a hematopoietic effect that lasts for not less than seven days. The invention provides a pharmaceutical composition containing, in an amount equal to not less than 50% of the total erythropoietin, erythropoietin to which two or more water-soluble long-chain molecules are added. The invention also provides a pharmaceutical composition containing erythropoietin to which a water-soluble long-chain molecule is added, wherein the water-soluble long-chain molecule has a molecular weight of not less than 30 kDa. The invention further provides a pharmaceutical composition containing erythropoietin to which a water-soluble long-chain molecule is added, wherein the water-soluble long-chain molecule has a branched chain.
