Human erythropoietin (EPO) is a glycoprotein hormone secreted from the kidney and controls red blood cell production. EPO has a wide clinical use in the treatment of anemia associated with renal disease, certain chronic diseases and anemia related to chemotherapy and radiotherapy. One major issue regarding the clinical use of EPO is its relatively short half-life due to its clearance by glomerular filtration. Thus the therapeutic protocol used in the treatment of patient required frequent injections of EPO. To address this issue, we constructed a chimeric gene that contains the sequence of the carboxyl-terminal peptide (CTP) of human chorionic gonadotropin (hCG) subunit bearing four O-linked oligosaccharide recognition sites and the coding sequence of human EPO cDNA. Fusing the CTP to the carboxyl-terminal of EPO did not affect secretion, receptor binding affinity or in vitro bioactivity. However, both in vivo potency and half-life of EPO-CTP were significantly enhanced. A single injection dose (660 IU/kg) of EPO Wild-type (EPO-WT) administered once a week had no significant effect on haematocrit levels. However, EPO-CTP administered as a 660 IU/kg once a week was effective as well as the same total dose of EPO-WT administered as 220 IU/kg 3 times a week. This may emphasize the importance of sustained blood levels rather than total dose of administration for in vivo bioactivity. These data established the rational for using this chimera as a long-acting EPO analog. The therapeutic efficacy of EPO-CTP analog needs to be established in higher animals and in human clinical trials.