The aim of this study was to investigate the therapeutic effects of methyl dehydroabietate (mDA) on adipocyte differentiation in 3T3-L1 preadipocytes and obesity characteristics induced by high-fat diet (HFD) in mice. Adipocyte differentiation in 3T3-L1 cells was evaluated after 14 days of incubation with mDA. mDA enhanced adipocyte differentiation in 3T3-L1 cells. For the in vivo evaluation, five-week-old male C57BL/6J mice were fed HFD or normal CE-2 diet (control) for eight weeks. During the experimental period, mice were administered mDA (50 mg/kg, p.o.) as an olive oil emulsion (containing 10% ethanol), and body weights were measured weekly. At the end of the experiment, the mice were euthanized after 16 h fasting period, and plasma samples were collected. The liver, kidney, and epididymal adipose tissues were collected and weighed. It significantly decreased body weight, adipose tissue weight, and plasma levels of glucose, insulin, leptin, and pro-inflammatory cytokines compared with that in the HFD group, and markedly reduced the impairment in glucose tolerance in obese mice. Furthermore, mDA reduced HFD-induced adipocyte hypertrophy and the formation of hepatic lipid droplets. Moreover, it induced the expression of proliferator-activated receptor alpha (PPARα) in the liver and PPARγ in the adipose tissues. Our findings demonstrate that mDA reduces obesity-induced glucose and insulin tolerance by inducing PPAR expression.