Objective To explore the changes and clinical significance of serum erythropoietin (EPO) in patients with secondary polycythemia. Methods The serum EPO levels in 32 secondary polycythemia patients, 15 polycythemia vera patients and 30 normal controls were determined by enzyme-linked immunosorbent assay. Results The median serum levels of EPO in secondary polycythemia patients were significantly higher than that of in polycythemia vera patients and healthy normal controls (P<0.01). The receiver operating characteristics curve analysis revealed that EPO had a significantly higher area under the curve, while the cut-off value was set to 22.43 mIU/mL with a sensibility and specificity of 71.88% and 82.22%. The serum EPO level had a positive correlation with RBC in secondary polycythemia patients (r=0.825, P<0.01). There was positive correlation between the serum levels of EPO and Hb concentration (r=0.772, P<0.01)．Conclusion The serum EPO is peculiarly present in secondary polycythemia patients, and would be used as a sensitive parameter for the diagnosis of secondary polycythemia.