A lipase from Aeromonas sp. LPB 4, a psychrotophile isolated from a sea sediment was purified and characterized. The lipase was purified 53.5 fold to a homogeneous state by acetone precipitation and QAE sephadex column chromatography and its molecular weight was determined to be 50 kDa by SDS-PAGE. The enzyme exhibited maximum activity at 10$^{circ}C$ and was stable at temperatures lower than 50$^{circ}C$. This lipase favored substrates containing medium carbon chain of acyl group, while too low and high carbon chain decreased its activity. The lipolytic activity of purified lipase was slightly increased by the addition of 0.1% detergent, but decreased by 1% of detergent. Butanol severely decreased the lipase activity while methanol increased the activity about 15%.