Sparassis crispa (SC), known as cauliflower mushroom, possesses a wide variety of health-promoting properties and a high content of β-glucans. Its nutritional properties are enhanced by fermentation. In this study, we examined the efficacy of Lactobacillus-fermented (lacto-fermented) SC against obesity using a zebrafish model. We first fermented SC by Lactobacillus paracasei, denoted as lacto-fermented SC (L-SC), for 48 h and then orally administered SC or L-SC to diet-induced obese zebrafish for 4 weeks. Results demonstrated that the L-SC group (20 μg/gBW/day) significantly (P < .01) suppressed body weight gain and ameliorated lipid accumulation in liver tissues, whereas SC did not exhibit antiobesity effects. We further performed expression analysis of genes related to lipid metabolism in the liver and visceral adipose tissues (VAT) in L-SC-administered fish. In liver tissues, L-SC upregulated (P < .05) expression of genes involved in peroxisome proliferator-activated receptor alpha pathways, suggesting that the lipid-lowering property of L-SC is caused by activation of beta-oxidation. In VAT, L-SC did not show significant changes between the experimental groups. No difference was observed between the β-glucan contents of SC (43.8 g/100 g) and L-SC (44.3 g/100 g); however, β-glucan levels in the hot-water extracts increased 20-fold in L-SC (37.2 g/100 g) compared with those in SC (1.8 g/100 g). In summary, lacto-fermentation of SC enhances its lipid-lowering property and can prevent hepatic steatosis through activation of beta-oxidation. Dietary supplementation of fermented L-SC as a functional food may be suitable for obesity prevention and reduction in the prevalence of obesity-related diseases.