The prevalence of obesity has been increasing worldwide, and its pathogenesis is closely related to preadipocyte differentiation. Because the presence of obesity increases the risk of chronic disease, it is important to decrease excessive body fat accumulation. This study aimed to demonstrate the anti-adipogenesis and anti-obesity effects of gongmi tea and gongmi so extract. The 3T3-L1 preadipocyte cell line was stained with Oil red O, and the expression levels of peroxisome proliferator-activated receptor- (PPAR), adiponectin, and fatty acid-binding protein 4 (FABP4) were evaluated via Western blot analysis. A mouse model of obesity was developed by feeding C57BL/6 male mice a high-fat diet (HFD). Gongmi tea or gongmi so extract was orally administered at a dose of 200 mg/kg for 6 weeks. The mouse body weight was measured weekly during the study period, and the epididymal adipose tissue weight and blood serum were analyzed at the end of the study period. The gongmi tea and gongmi so extract did not exhibit toxicity in mice. Oil red O staining showed that gongmi tea significantly decreased excessive body fat accumulation. In addition, gongmi tea (300 g/mL) significantly downregulated adipogenic transcription factors, such as PPAR, adiponectin, and FABP4. In vivo tests indicated that oral administration of gongmi tea or gongmi so extract to C57BL/6 mice with HFD-induced obesity effectively decreased their body weight and epididymal adipose tissue. Gongmi tea and gongmi so extract have potent in vitro anti-adipogenic effects in 3T3-L1 cells and in vivo anti-obesity effects in mice with HFD-induced obesity.