Introduction: The patient-to-nurse ratio is highly variable among dialysis facilities. However, there is little known about the association between nurse caseload and hemodialysis (HD) patient outcomes. We evaluated the association between patient-to-nurse ratio and mortality in the Korean patients undergoing HD. Methods: We used HD quality assessment data and National Health Insurance Service claim data from the year of 2013 for collecting demographic and clinical data. Altogether, 21,817 patients who participated in the HD quality assessment in 2013 were included in the study. Nurse caseload was defined as the number of HD sessions performed by a nurse per working day. The patients were divided into two groups according to the nurse caseload as follows: low nurse caseload group (≤6.0) and high nurse caseload group (>6.0). We analyzed mortality risk based on nurse caseload using the Cox proportional hazard model. Results: The mean age was 59.1 years, and males accounted for 58.5%. The mean hemoglobin was 10.6 g/dL and albumin was 3.99 g/dL. At the mean follow-up duration of 51.7 (20.6) months, the ratio between low and high groups was 69.6% (15,184 patients) versus 30.4% (6,633 patients). The patients in the high nurse caseload group were older and showed lower levels of hemoglobin, albumin, calcium, and iron saturation and higher levels of phosphorus than those in the low nurse caseload group. A high nurse caseload was associated with a lower survival rate. In the adjusted Cox analysis, a high nurse caseload was an independent risk factor for all-cause mortality (hazard ratio 1.08; 95% confidence interval, 1.02–1.14; p = 0.01). Conclusion: High nurse caseload was associated with an increased mortality risk among the patients undergoing HD. Further prospective studies are needed to determine whether a caseload of nursing staff can improve the prognosis of HD patients.