BACKGROUND: Ginsenoside Rg1 is a class of steroid glycoside and triterpene saponin in Panax ginseng. Many studies suggest that Rg1 suppresses adipocyte differentiation in 3T3-L1. However, the detail molecular mechanism of Rg1 on adipogenesis in 3T3-L1 is still not fully understood. METHODS: 3T3-L1 preadipocyte was used to evaluate the effect of Rg1 on adipocyte development in the differentiation in a stage-dependent manner in vitro. Oil Red O staining and Nile red staining were conducted to measure intracellular lipid accumulation and superoxide production, respectively. We analyzed the protein expression using Western blot in vitro. The zebrafish model was used to investigate whether Rg1 suppresses the early stage of fat accumulation in vivo. RESULTS: Rg1 decreased lipid accumulation in early-stage differentiation of 3T3-L1 compared with intermediate and later stages of adipocyte differentiation. Rg1 dramatically increased CAAT/enhancer binding protein (C/EBP) homologous protein-10 (CHOP10) and subsequently reduced the C/EBPß transcriptional activity that prohibited the initiation of adipogenic marker expression as well as triglyceride synthase. Rg1 decreased the expression of extracellular signal-regulated kinase 1/2 and glycogen synthase kinase 3ß, which are also essential for stimulating the expression of CEBPß. Rg1 also reduced reactive oxygen species production because of the downregulated protein level of nicotinamide adenine dinucleotide phosphate hydrogen (NADPH) oxidase 4 (NOX4). While Rg1 increased the endogenous antioxidant enzymes, it also dramatically decreased the accumulation of lipid and triglyceride in high fat diet-induced obese zebrafish. CONCLUSION: We demonstrated that Rg1 suppresses early-stage differentiation via the activation of CHOP10 and attenuates fat accumulation in vivo. These results indicate that Rg1 might have the potential to reduce body fat accumulation in the early stage of obesity.