Objective: This retrospective cohort study enrolled DKD patients from two South Korean tertiary-referral centers. Antidiabetic medication history was reviewed. Primary outcomes were all-cause mortality and DFU events; secondary outcomes included hospitalization, amputation, composite of amputation or vascular intervention, and Wagner Grade >3. Multivariate cox analysis and Propensity score matching (PSM) was used to balance baseline intergroup differences between metformin users and metformin non-users. Methods: Among 10,832 patients (4,748 metformin users; 6,084 metformin non-users), the 117·5±66·9 months follow-up period, all-cause mortality rate and DFU incidence were, 37·1%, and 5·2%, respectively. Fully adjusted multivariate Cox analysis showed that metformin users had a lower all-cause mortality (adjusted hazard ratio 0·63; 95% confidence interval 0·58–0·68; p<0·001) and DFU events (0·39; 0·31–0·48; p<0·001). After PSM, metformin users showed lower all-cause mortality (0·61; 0·55–0·67; p<0·001), DFU events (0·42; 0·32 –0·56; p<0·001), and secondary outcomes (hospitalization, amputation, composite of amputation or vascular intervention, and DFU with Wagner Grade >3). Results: Metformin therapy in DKD patient can lower all-cause mortality, DFU incidence, and DFU progression. Conclusions: Objective: Diabetic foot ulcer (DFU) and diabetic kidney disease (DKD) are diabetes-related microvascular complications strongly correlated with high morbidity and mortality. Metformin potentially confers a wound-healing advantage, although there are no well-established evidence. We first time investigated the effect of metformin on DFU among large retrospective cohort of DKD patients. Methods: This retrospective cohort study enrolled DKD patients from two South Korean tertiary-referral centers. Antidiabetic medication history was reviewed. Primary outcomes were all-cause mortality and DFU events; secondary outcomes included hospitalization, amputation, composite of amputation or vascular intervention, and Wagner Grade >3. Multivariate cox analysis and Propensity score matching (PSM) was used to balance baseline intergroup differences between metformin users and metformin non-users. Results: Among 10,832 patients (4,748 metformin users; 6,084 metformin non-users), the 117·5±66·9 months follow-up period, all-cause mortality rate and DFU incidence were, 37·1%, and 5·2%, respectively. Fully adjusted multivariate Cox analysis showed that metformin users had a lower all-cause mortality (adjusted hazard ratio 0·63; 95% confidence interval 0·58–0·68; p<0·001) and DFU events (0·39; 0·31–0·48; p<0·001). After PSM, metformin users showed lower all-cause mortality (0·61; 0·55–0·67; p<0·001), DFU events (0·42; 0·32 –0·56; p<0·001), and secondary outcomes (hospitalization, amputation, composite of amputation or vascular intervention, and DFU with Wagner Grade >3). Conclusions: Metformin therapy in DKD patient can lower all-cause mortality, DFU incidence, and DFU progression.