Several severity scales have been documented to predict the short-term mortality of septic patients. However, the predictive efficacies of different severity scales in the long-term mortality of the elderly have yet to be evaluated. In the retrospective study, a cohort of 4,370 elderly (≥65 years) septic patients admitted to the intensive care unit (ICU) were divided into three different age groups, i.e., the younger-old group (65 years ≤ age <75 years), the older-old group (75 years ≤ age <85 years) and the oldest-old group (age ≥85 years). Five scales, including the Simplified Acute Physiology Score II (SAPS II), the Oxford Acute Severity of Illness Score (OASIS), the Modified Logistic Organ Dysfunction System (MLODS), the Systemic Inflammatory Response Syndrome (SIRS) and Sequential Organ Failure Assessment (SOFA), were used for disease severity evaluations. The Kaplan-Meier survival curve, and the area under the receiver operating characteristic curve (AUC) were used to assess prognostic values of the long-term mortality of each severity scale. Compared with patients in the oldest-old group, those in the younger-old and the older-old groups had higher scores of SAPS II and OASIS, indicating more serious illness and worse prognosis. The survival time of patients was inversely related to age; the mean survival time was the longest in the youngerold group, followed by the older-old group and the oldest-old group. SAPS II had the best prognostic value (AUC: 0.648 for SAPS II, 0.579 for MLODS, 0.577 for SOFA, 0.612 for OASIS and 0.515 for SIRS, P<0.01) for the 4-year all-cause mortality. Elderly patients with an SAPS II score >43 had a lower survival rate regardless of age. The long-term mortality of elderly patients with sepsis is increased with age. SAPS II can better predict the long-term prognosis of elderly septic patients in ICU.