Abstract: Doxorubicin (DOX) is an anthracycline antibiotic widely used in the treatment of certain types of tumors. However, DOX have some serious side effects in the body after long-term use, especially acute and chronic cardiotoxicity. This study explored the protective effect of tanshinone I (Tan I) on acute cardiotoxicity induced by DOX and its underlying molecular mechanisms. In vivo and in vitro acute cardiotoxicity models were established by injecting DOX (6 mg·kg^-1, twice per week) into the tail vein of C57 mice and stimulating H9C2 cardiomyocytes with DOX. In in vivo experiments, Tan I (10 mg·kg^-1) was administered daily by oral 5 days before the tail vein injection, till the end of the experiment. The effects of Tan I on mice heart function, myocardial tissue morphology and serological indicators were detected. Animal welfare and experimental procedures followed the regulations of the Animal Ethics Committee of Beijing University of Traditional Chinese Medicine. In in vitro experiments, the specific mechanism of Tan I against oxidative stress was further studied. Immunofluorescence was used to detect the expression of Nrf2 and its transcription into the nucleus. In addition, the levels of oxidative stress related proteins, protein kinase B (Akt), nuclear erythroid factor 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1) and NAD(P)H quinone dehydrogenase 1 (NQO1), were detected by Western blot. Finally, AutoDock software was used for molecular docking verification. The results showed that Tan I significantly improved cardiac function in mice. Meanwhile, the expression levels of creatine kinase-MB (CK-MB) and lactic dehydrogenase (LDH) in serum were decreased. Immunofluorescence results indicated that Tan I could increase Nrf2 expression level in H9C2 cells and promote Nrf2 entry into the nucleus. Western blot results also indicated that the levels of oxidative stress related proteins, P-Akt, Nrf2, HO-1 and NQO1 in DOX plus Tan I group were significantly increased compared with DOX group. These results suggest that Tan I can alleviate DOX-induced acute cardiotoxicity by inhibiting oxidative stress through up-regulating the Akt-Nrf2 pathway, thereby alleviating DOX-induced acute myocardial injury.