Background: The upregulation of reactive oxygen species (ROS) is a primary cause of cardiomyocyte apoptosis in Diabetes cardiomyopathy (DCM). Mitofusin-2 (Mfn-2) is a key protein that bridges the mitochondria and endoplasmic reticulum(ER). Hydrogen sulfide (H₂S)-mediated cardioprotection is related to antioxidant effects. The present study demonstrated that H₂S inhibited the interaction between the ER and mitochondrial apoptotic pathway. Methods: This study investigated cardiac function, ultrastructural changes in the ER and mitochondria, apoptotic rate using TUNEL and the expression of ER stress-associated proteins and mitochondrial apoptotic proteins in cardiac tissues in STZ-induced type I diabetic rats treated with or without NaHS (donor of H₂S). Mitochondria of cardiac tissues were isolated, and MPTP opening and cytochrome C (cyt C) and Mfn-2 expression were also detected. Results: Our data showed that hyperglycemia decreased the cardiac function by Ultrasound Cardiogram, and the administration of exogenous H₂S ameliorated these changes. We demonstrated that the expression of ER stress sensors and apoptotic rates were elevated in cardiac tissue of DCM and cultured H9C2 cells, but the expression of these proteins was reduced following exogenous H₂S treatment. The expression of mitochondrial apoptotic proteins, cyt C and mPTP opening were decreased following treatment with exogenous H₂S. In our experiment, the expression and immunofluorescence of Mfn-2 were both decreased after transfection with Mfn-2-siRNA. Conclusion: Hyperglycemia stimulated ER interactions and mitochondrial apoptotic pathways, which were inhibited by exogenous H₂S treatment through the regulation of Mfn-2 expression.