The effects of self-assembled polysaccharide nanogels on colloidal and thermal stability of lipase from Pseudomonas cepacia were investigated. The enzyme activity, especially k(cat), drastically increased in the presence of nanogels of cholesterol-bearing pullulan (CHP). The thermostability of lipase complex increased because the denaturation temperature of lipase increased by more than 20 degrees C by complexation with CHP nanogels. Lipase denaturation and aggregation upon heating was effectively prevented by complexation with CHP nanogels. Moreover, complexation with CHP nanogels protected lipase from lyophilization-induced aggregation. Nano-encapsulation with CHP nanogel is a useful method for colloidal and thermal stabilization of unstable enzyme.