Abstract: Terpinen-4-ol (T4O) is a bioactive monoterpenoid with significant cardiovascular pharmacological activity. This study investigated T4O's protective effects against high glucose (HG) induced injury in rat cardiomyocytes (H9C2) and its impact on silencing the sirtuin 1 (SIRT1)/peroxisome proliferator-activated receptor-γ (PPARγ) signaling pathway. In the experiment, H9C2 cells were pre-incubated with different doses of T4O for 2 h, followed by co-incubation with HG for 48 h to create an injury model. Cell survival was determined using the MTT assay. Intracellular reactive oxygen species (ROS) levels were detected using the fluorescent probe DCFH-DA. Apoptosis rates were detected using flow cytometry. Mitochondrial membrane potentials were observed using JC-1 staining. Western blot was used to detect the expression levels of the apoptosis-related proteins Bcl-2, Bax, Caspase-9, and Caspase-3, as well as SIRT1 and PPARγ. Immunofluorescence was used to observe the localization and expression of SIRT1 and PPARγ. Silencing SIRT1 expression in H9C2 cells was achieved by SIRT1 siRNA transfection. The effects of T4O on ROS content, apoptosis rate, mitochondrial membrane potential, and expression of the aforementioned proteins in HG-induced H9C2 cells were then observed. Compared to the HG group, T4O significantly improved HG-induced injury to H9C2 cells. It decreased ROS levels and the apoptosis rate, increased the mitochondrial membrane potential, and down-regulated the expression levels of the Caspase-9 and Caspase-3 proteins induced by HG. Meanwhile, it increased the Bcl-2/Bax ratio and SIRT1 and PPARγ expression levels (P < 0.05, P < 0.01). After SIRT1 was silenced, compared with the negative control + HG group, the SIRT1 siRNA + HG group exhibited significantly increased intracellular ROS levels and apoptosis rates, reduced mitochondrial membrane potential, and upregulated of Caspase-9 and Caspase-3 protein expression. while the Bcl-2/Bax ratio and expression levels of SIRT1 and PPARγ were further downregulated (P < 0.05, P < 0.01). Co-treatment with SIRT1 silencing and T4O reversed the protective effect of T4O against H9C2 cells damage. In conclusion, T4O ameliorates HG-induced injury to H9C2 cells by activating the SIRT1/PPARγ signaling pathway. This provides a new idea and potential target for developing anti-myocardial injury drugs.