Background: A growing number of older patients are undergoing surgeries. The reliable pre-operative predictive factors of surgical mortality among older patients remained unclear. This study compared the predictive factors for 30-day survival in patients over 90 years old after their non-cardiac surgery. Methods: A retrospective study at Nippon Medical School hospital was performed for patients aged >90 years who underwent non-cardiac surgeries between 2010 and 2020. Measurements included age, gender, American Society of Anesthesiologists physical status (ASA-PS), pre-operative Charlson score, pre-operative fall risk assessment, Eastern Cooperative Oncology Group performance status (ECOG-PS), the modified 5item frailty index (mFI-5), the presence of intra-operative transfusion, post-operative complications, and 30-day survival post-surgery. Results: A total of 327 cases of elective surgery and 149 cases of emergency surgery were examined. The non-survival group (n=20, 4.2%) had significantly worse pre-operative ASA-PS in emergency cases (non-survival vs. survivor group, 2.8 [2-3] vs. 2.3 [1-4], p=0.045), ECOG-PS (3.0 [2-4] vs. 1.0 [0-4], p<0.001), and mFI-5 values (3.0 [1-4] vs.1.0 [0-3], p<0.001), more emergency cases (75.0% vs. 36.2%, p=0.004), and a greater need for intra-operative transfusion (55.0% vs. 13.4%, p<0.001). Among the frailty assessment methods, ECOG-PS was the most efficient for 30-day mortality (area under curve, ECOG-PS: 0.98, p<0.001; mFI-5: 0.86, p<0.001; Charlson score: 0.53, p=0.71; fall risk assessment: 0.55, p=0.44). Kaplan-Maier curves and a multivariate logistic regression analysis demonstrated that ECOG-PS>3 was significantly associated with 30day mortality (ECOG-PS: Kaplan-Maier curve, p<0.001, Log-rank test; odds ratio 1.71, 95%CI: 1.35-2.16, p<0.001).