Crude lipase from Rhizopus sp. was moderately stable against heat treatment at 45 degreesC. However, after incubation for 1 h at 25 degreesC with Streptoverticillium transglutaminase (MTG), the half-life of crude lipase in the heat treatment was increased more than 10-fold compared to that of untreated one. The result can be ascribed by the MTGase-mediated crosslinking of contaminating proteins that affect the apparent thermostability of lipase in the crude sample.