Betulinic acid is a pentacyclic triterpenic acid that exists naturally in many kinds of food and has many biological functions. The present study investigated the antiobesity properties of betulinic acid and possible mechanisms by which betulinic acid functions. To examine the antilipase function of betulinic acid, the ability of betulinic acid to inhibit pancreatic lipase activity in vitro and to prevent the elevation of plasma triacylglycerol levels was tested after oral administration of a lipid emulsion in rats. In addition, the lipolytic effects of betulinic acid were assayed in rat adipose tissues. The activity of cAMP-dependent phosphodiesterase was also measured in vitro. Betulinic acid inhibited pancreatic lipase activity in a dose-dependent manner at concentrations of 1.5–100 µ m (IC50 value of 21.10 µ m) and prevented the elevation of plasma triacylglycerol levels 2 h after oral administration of the lipid emulsion at a dose of 100 mg/kg. In addition, betulinic acid had a strong lipolytic effect, which was mediated by cAMP-dependent phosphodiesterase inhibition. In conclusion, betulinic acid may exert antiobesity effects by directly inhibiting pancreatic lipase, which would prevent the absorption of lipid from the small intestine. In addition, it was found that betulinic acid may further accelerate fat mobilization by enhancing the levels of lipolysis in adipose tissues. Copyright © 2011 John Wiley & Sons, Ltd.