This study aimed to investigate the effects of fermented garlic extract (FGE) by Lactobacillus plantarum BL2 in high fat diet (HFD)-induced hepatic steatosis. FGE administration increased insulin sensitivity and decreased serum lipid levels. Moreover, treatment with FGE effectively decreased hepatic lipid level, resulting in reduction of hepatic steatosis compared to that with non-fermented garlic extract (NFGE). These functions of FGE were associated with AMPK-mediated stimulation of hepatic lipolysis through upregulation of PPARα and suppression of hepatic lipogenesis, partly via downregulation of SREBP-1c, FAS, and SCD-1. Significant improvement in HFD-induced steatosis following administration of FGE was closely linked to its enhanced antioxidant activity of the enriched organosulfur compounds, cycloalliin and SAC, by fermentation, regarding hepatic redox status and oxidative damage. This study validated the advanced therapeutic value of FGE in the prevention of diet-induced non-alcoholic fatty liver disease.