Background. β 2 -Microglobulin (β 2 -M) is recognized as a surrogate marker of middle-molecule uraemic toxins and is a key component in the genesis of dialysis-associated amyloidosis. Few studies have evaluated the association of β 2 -M levels with clinical outcome in dialyzed patients. Methods. The prognostic implication of serum β 2 -M levels for the survival of haemodialysis patients was examined in 490 prevalent haemodialysis patients (60.1 Âą 11.8 years, haemodialysis duration of 87.4 Âą 75.7 months, 288 males and 202 females; 24% diabetics). The patients were divided into two groups according to their serum β 2 -M levels: lower β 2 -M group (n = 245) with serum β 2 -M <32.2 mg/L (the median serum β 2 -M) and higher β 2 -M group (n = 245) with that âĽ32.2 mg/L. Results. During the follow-up period of 40 Âą 15 months, there were 91 all-cause deaths, and out of them, 36 were from cardiovascular diseases. Kaplan-Meier analysis revealed that all-cause mortality in the higher β 2 -M group was significantly higher compared to that in the lower β 2 -M group (P < 0.001). Multivariate Cox proportional hazards analyses showed that serum β 2 -M level was a significant predictor for all-cause mortality (hazard ratio, 1.05; 95% CI, 1.01-1.08; P = 0.005), and for non-cardiovascular mortality (hazard ratio, 1.06; 95% CI, 1.02-1.10; P = 0.006), after adjustment for age, gender, haemodialysis duration, the presence of diabetes, serum albumin and serum C-reactive protein.Conclusion. These results demonstrate that the serum β 2 -M level is a significant predictor of mortality in haemodialysis patients, independent of haemodialysis duration, diabetes, malnutrition and chronic inflammation, suggesting the clinical importance of lowering serum β 2 -M in these patients.