Monodisperse thermosensitive PS-NIPA core-shell particles composed of a PS core and a cross-linked PNIPA shell can be successfully synthesized by a novel method: photoemulsion polymerization. Cryo-TEM images indicate clearly the core-shell morphology of the PS-NIPA particles: A homogeneous regular PNIPA shell has been affixed on the spherical PS core. DLS measurements indicate that the obtained PS-NIPA latex particles are thermosensitive. The shell of PNIPA networks with different cross-linking densities can shrink and re-swell with temperature and the volume transition temperature is around 32 degrees C in all cases.