Abstract： Objective To investigate the significance of serum CD25 / serum ferritin in the diagnosis of lymphoma-associated hemophagocytic syndrome (LAHS),so as to provide the clinical basis for improving its recognition and giving effective therapy. Methods The serums were collected from 70 patients with hemophagocytic syndrom in Beijing Friendship Hospital, Capital Medical University during the period from October 2008 to June 2011, including 31 LAHS cases and 39 other disease-associated HPS cases. The serum CD25 level in HPS patients was measured with enzyme-linked immunosorbent assay (ELISA), and the serum ferritin was measured on the same day. Then the serum CD25/ferritin ratio was calculated and the differences of the serum CD25, serum ferritin and serum CD25/ferritin ratio between two groups were compared. Results The variance of serum CD25 [(15760.52±7851.74) pg/ml vs (12727.41±11285.28) pg/ml,t=-1.78,P=0.075] and serum ferritin levels (1750.00 ng/ml vs 2947.00 ng/ml,Z=-1.490,P=0.136)were not statistically significant between two groups,while the serum CD25/serum ferritin ratio in LAHS patients was significantly higher than the other group(8.57×10-3 vs 2.84×10-3,Z=-2.106,P=0.035).Conclusion The serum CD25/ serum ferritin ratio is statistically higher in LAHS patients, which might be a novel useful marker for predicting underlying malignant lymphoma in HPS patients.