BACKGROUND Some studies have shown that the estimated glomerular filtration rate (eGFR) at the time of initiating dialysis was associated with mortality. However, the relationship between ratio of blood urea nitrogen to serum creatinine (BUN/Cr) and mortality is unknown. METHODS The study was a multicenter, prospective cohort analysis including 1520 patients. Patients were classified into four quartiles based on the BUN/Cr ratio at the dialysis initiation, with Q1 having the lowest ratio and Q4 the highest. All-cause mortality after initiating dialysis was compared using the log-rank test. All-cause mortality of Q1, Q2, and Q3 was compared with that of Q4 using multivariate Cox proportional hazard regression analysis. Moreover, we compared the renal parameters including BUN/Cr ratio, eGFR, and creatinine clearance for sensitivity and specificity using receiver operative characteristic (ROC) curve. RESULTS Significant differences were observed in all-cause mortality among the four groups (p < 0.001). Multivariate analysis revealed that all-cause mortality was significantly higher in Q4 than in Q1 [hazard ratio (HR) = 1.82, 95% confidence interval (CI) 1.24-2.67, p = 0.002]. The increase in BUN/Cr ratio was positively associated with mortality (HR 1.04, 95% CI 1.02-1.06, p = 0.002). The sensitivity and specificity of BUN/Cr ratio for 180, 365, 730, and 1095 days mortality ranged between 0.60-0.72 and 0.59-0.71, respectively. The area under the curve of BUN/Cr for all-cause mortality was the highest among the renal parameters. CONCLUSIONS The BUN/Cr ratio at the time of initiation of dialysis was associated with all-cause mortality.