OBJECTIVE This study investigated the effects of indole-3-carbinol (I3C), a cruciferous vegetable derivative, on obesity and its associated factors in high-fat-diet-induced obese (DIO) mice. METHODS Eighteen male C57BL/6 mice were randomly assigned to one of three groups: basal, high fat (HF), and HF + 5 mg/kg of I3C intraperitoneally (HFI). After 12 wk of treatment, obesity-associated factors, including body weight, organ weight, serum concentrations of glucose, triacylglycerol, insulin, and adipokines, and macrophage accumulation and lipid metabolism-associated factors in epididymal adipose tissue were measured. RESULTS Body weight and epididymal adipose tissue weight were greater (P < 0.01), and adipocytes were larger in the HF group than in the basal and HFI groups. Compared with the HF group, the HFI group had improved glucose tolerance, a higher serum adiponectin concentration, lower serum glucose, triacylglycerol, insulin, and leptin concentrations, and less F4/80 expression in epididymal adipose tissue (P < 0.001). Furthermore, I3C treatment decreased acetyl coenzyme A carboxylase mRNA expression (P < 0.05) and increased peroxisome proliferator-activated receptor-γ protein expression (P < 0.05) in epididymal adipose tissue of DIO mice. CONCLUSIONS The I3C treatment decreased body weight and fat accumulation and infiltrated macrophages in epididymal adipose tissue of DIO mice, and these reductions were associated with improved glucose tolerance and with modulated expression of adipokines and lipogenic-associated gene products, including acetyl coenzyme A carboxylase and peroxisome proliferator-activated receptor-γ.