An inverse microemulsion polymerization was used to encapsulate lipase in polymer nanoparticles. The utilization of a non-ionic surfactant, polyoxyethylene-4-lauryl ether, in combination with sodium bis-2-ethylhexylsulfosuccinate reduced the charge density at the interfacial region of the microemulsion and thus favored the activity of lipase accommodated at the interfacial region of the microemulsion. At the optimized condition, 73.8 and 88.6 % of the original activity for lipase encapsulated in polyacrylamide and poly(N-isopropylacrylamide) (PNIPAM) nanoparticles were obtained. The lipase encapsulated in polyacrylamide nanoparticles exhibited a tenfold increase in the half-life time of enzyme activity at 50 A degrees C. The temperature-responsive property of PNIPAM provided a temperature-controlled activity for the encapsulated lipase.