BACKGROUND As glomerular filtration rate (GFR) decreases, serum phosphate level increases. Previous reports indicated that serum phosphate level was associated with mortality in patients on dialysis. However, few reports have examined the association using dialysis initiation as the baseline period. METHODS This was a multicenter prospective cohort analysis including 1492 patients. Patients were classified into four quartiles based on the serum phosphate level at dialysis initiation, with Q1 being the lowest and Q4 the highest. All-cause mortality after dialysis initiation was compared using the log-rank test. The propensity score represented the probability of being assigned to group Q1 or Q2-4. All-cause mortality was compared in propensity score-matched patients by using the log-rank test for Kaplan-Meier curves. All-cause mortality of Q1 was compared with that for Q2-4 using multivariate Cox proportional hazard regression analysis. All-cause mortality was also determined among stratified groups with or without use of phosphate binders. RESULTS Significant differences in cumulative survival rates were observed between the four groups (p < .001). After propensity score-matching, mortality was significantly higher in the Q1 group than the Q2-4 group (p = .046). All-cause mortality was significantly higher in the Q1 group after adjustment for history of CAD (hazard ratio [HR] = 0.76, 95% confidence interval [CI]: 0.58 - 1.00, p = .048). However, there was no significant difference between the two groups after adjustment for estimated GFR. CONCLUSIONS The serum phosphate level at the time of dialysis initiation was associated with all-cause mortality. However, the serum phosphate level was dependent on the renal function.