Objective To explore whether the decrease of free triiodothyronine (FT3) has early predictive value in infection-induced multiple organ dysfunction syndrome in the elderly (i-MODSE). Methods The clinical data of 755 elderly infected patients (≥65 years old) who were discharged from the Department of Geriatrics, First Affiliated Hospital of Air Force Military Medical University from January 2017 to December 2021 were retrospectively analyzed. According to the occurrence of multiple organ dysfunction syndrome (MODS) during hospitalization, the patients were divided into MODS group (n=80) and control group (n=675). The effects of demographic characteristics and laboratory tests, including FT3, on i-MODSE were analyzed. The data were analyzed by SPSS statistics 26.0. Data comparison between two groups was performed using student′s t test, Mann-Whitney U test or Chi-square test depending on different data types. Binary logistic regression was used to analyze the influencing factors of i-MODSE. Results Among the 755 patients, the incidence of MODS was 10.60% (80/755). FT3 level was significantly lower in the MODS group than the control group [(2.67±0.87) vs (3.40±0.79) pmol/L; P<0.001]. Logistic regression analysis showed that FT3 decline was an independent risk factor for the occurrence of MODS in elderly infected patients (OR=4.748,95%CI 2.387-9.443; P<0.001). Conclusion FT3 decline is an independent risk factor for the occurrence of MODS in elderly patients with infection, and can be used to predict i-MODSE in the early stage.