In this work, the poly(methyl methacrylate-co-methacrylic acid)/poly(methacrylic acid-co-N-isopropylacrylamide) thermosensitive composite semi-hollow latex particles was synthesized by three processes. The first process was to synthesize the poly(methyl methacrylate-co-methacrylic acid) (poly (MMA-MAA)) copolymer latex particles by the method of soapless emulsion polymerization. The second process was to polymerize methacrylic acid (MAA), N-isopropylacrylamide (NIPAAm), and crosslinking agent, N,N-methylenebisacrylamide, in the presence of poly(MMA-MAA) latex particles to form the linear poly(methyl methacrylate-co-methacrylic acid)/crosslinking poly(methacrylic acid-co-N-isopropylacrylamide) (poly(MMA-MAA)/poly(MAA-NIPAAm)) core-shell latex particles with solid structure. In the third process, part of the linear poly(MMA-MAA) core of core-shell latex particles was dissolved by ammonia to form the poly(MMA-MAA)/poly(MAA-NIPAAm) thermosensitive semi-hollow latex particles. The morphologies of the semi-hollow latex particles show that there is a hollow zone between the linear poly(MMA-MAA) core and the crosslinked poly(MAA-NIPAAm) shell. The crosslinking agent and shell composition significantly influenced the lower critical solution temperature of poly(MMA-MAA)/poly(MAA-NIPAAm) semi-hollow latex particles. Besides, the poly(MMA-MAA)/poly(MAA-NIPAAm) thermosensitive semi-hollow latex particles were used as carriers to load with the model drug, caffeine. The processes of caffeine loaded into the semi-hollow latex particles appeared four situations, which was different from that of solid latex particles. In addition, the phenomenon of caffeine released from the semi-hollow latex particles was obviously different from that of solid latex particles. (c) 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3441-3451