Abstract: AIM To investigate the levels of serum xanthine oxidase (XO) in heart failure patients with reduced ejection fraction (EF) and to study the possible correlations of serum XO levels with heart fatty acid binding protein (H-FABP) and matrix metalloproteinases-2, -9 (MMP-2, MMP-9). METHODSA total of 80 patients who were hospitalized or undergoing physical examination at the People’s Hospital of Xinjiang Uygur Autonomous Region were divided into heart failure with decreased EF group (n=40) and control group (n=40). Height, weight and blood pressure were measured in all patients. Fasting venous blood samples were collected and the levels of serum XO, H-FABP, MMP-2 and MMP-9 were tested by enzyme-linked immunosorbent assay (ELISA). RESULTSCompared with control group, serum XO levels in heart failure group significantly increased (P<0.05). In heart failure group, serum XO levels were positively correlated with H-FABP, MMP-2 and MMP-9 (r=0.787, 0.838 and 0.864, respectively; P<0.01). Multiple linear stepwise regression analysis showed that H-FABP and MMP-2 and MMP-9 were independent factors affecting serum XO levels (P<0.01). CONCLUSIONSerum XO levels in heart failure patients with reduced ejection fraction decrease significantly and serum XO levels are associated with heart fatty acid binding protein and matrix metalloproteinases-2, -9.