Obesity is a key contributing risk factor to cardiovascular disease, certain cancers, and diabetes. Much effort has being made to investigate potential inhibitors against lipase from natural products. The ethyl acetate (EA) extract of Ecklonia cava (EC) were tested for their ability to inhibit pancreatic lipase activity in vitro. The 22 sub-fractions from EA extract were separated using silica gel column chromatography. Among the sub-fractions, the EA6 sub-fraction exhibited the highest inhibitory activity. Dieckol compound was isolated from the EA6 sub-fraction, which inhibited the lipase activity in a concentration-dependent manner with $IC_{50}$ value at 0.26 mg/mL. These results suggest that EC has potential as a natural anti-obesity agent.