Hydrophobic poly(lactic acid) nanospheres were fabricated and used as an additive during the polymerization and gelation process of temperature-sensitive poly(N-isopropylacrylamide) (PNIPAAm) hydrogels. The influence of hydrophobic additive on properties of PNIPAAm hydrogels was examined. The interior morphology studied by scanning electron microscopy revealed that the hydrophobic additive induced a macroporous structure in the resulting PNIPAAm hydrogels. Results demonstrate that the hydrophobic additive acts as a pore-forming agent like conventionally used hydrophilic additive does during the gelation process. Because of the macroporous network and incorporated additives, the temperature-sensitive characteristics, particularly the equilibrium swelling ratio at room temperature and shrinking rate upon temperature increase of modified PNIPAAm hydrogels, are significantly improved. (c) 2005 Wiley Periodicals, Inc.