Garlic oil has been reported to protect the cardiovascular system; however, the effects and mechanisms behind the cardioprotection of garlic oil on diabetes-induced cardiaomyopathy are unclear. In this study, we used streptozotocin (STZ)-induced diabetic rats to investigate whether garlic oil could protect the heart from diabetes-induced cardiomyopathy. Wistar STZ-induced diabetic rats received garlic oil (0, 10, 50 or 100 mg kg−1 body weight) by gastric gavage every 2 days for 16 days. Normal rats without diabetes were used as control. Cardiac contractile dysfunction and cardiac pathologic hypertrophy responses were observed in diabetic rat hearts. Cardiac function was examined using echocardiography. In addition to cardiac hypertrophy-related mitogen-activated protein kinases (MAPK) pathways (e.g., p38, c-Jun N-terminal kinases (JNK) and extracellularly responsive kinase (ERK1/2)), the IL-6/MEK5/ERK5 signaling pathway was greatly activated in the diabetic rat hearts, which contributes to the up-regulation of cardiac pathologic hypertrophy markers including atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP), and leads to cardiac contractile dysfunction. Garlic oil treatment significantly inhibited the up-regulation in MAPK (e.g., p38, JNK and ERK1/2) and IL-6/MEK5/ERK5 signaling pathways in the diabetic rat hearts, reducing the levels of cardiac pathologic hypertrophy markers such as ANP and BNP, and improving the cardiac contractile function. Collectively, data from these studies demonstrate that garlic oil shows the potential cardioprotective effects for protecting heart from diabetic cardiomyopathy.