Purpose: This study was done to examine relationships between nurse staffing level and postsurgical patient outcomes using inpatient database from the National Health Insurance. Methods: Records of 111,491 patients who received one of 12 types of surgery between January and December, 2009 were identified and analyzed in this study. Nurse staffing level was measured using adjusted nurse staffing grades from 0 to 7. Patient outcomes were defined as in-hospital mortality, or pneumonia, sepsis, or urinary tract infection after surgery. Logistic regression analyses estimated by Generalized Estimation Model, were used to analyze the association between nurse staffing level and patient outcomes. Results: An inverse relationship was found between nurse staffing and patient mortality. Compared with patients who were cared for in hospitals with the highest nurse staffing (Grades 0-1), increases in the odds of dying were found in those with Grades 6-7 [OR (odds ratio)=2.99, 95% CI (confidence interval)=1.94-4.60], those with Grades 4-5 (OR=1.78, 95% CI=1.24-2.57) and those with Grades 2-3 (OR=1.57, 95% CI=1.25-1.98). Lower nurse staffing level was also associated with higher number of cases in pneumonia and sepsis. Conclusion: Policies for providing adequate nurse staffing is required to enhance quality of care and lead to better perioperative patient outcomes.