An object of the invention is to provide apharmaceutical composition that contains erythropoietin asthe active ingredient and has, when administered in humansand/or animals, a hematopoietic effect that lasts for notless than seven days. The invention provides apharmaceutical composition containing, in an amount equaltc not less than 50% of the total erythropoietin,erythropoietin to which two or more water-soluble long-chainmolecules are added. The invention also provides apharmaceutical composition containing erythropoietin towhich a water-soluble long-chain molecule is added, whereinthe water-soluble long-chain molecule has a molecularweight of not less than 30 kDa. The invention furtherprovides a pharmaceutical composition containingerythropoietin to which a water-soluble long-chain moleculeis added, wherein the water-soluble long-chain molecule hasa branched chain.
