Thermosensitive poly(N-isopropylacrylamide-co-acrylamide) microgel particles were prepared through precipitation polymerization. The diameters of the microgel particles were in the range of 220-270 nm and showed a monodispersion. The lower critical solution temperatures (LCST) of the microgel dispersions were measured by dynamic light scattering and turbidimetric analysis. The results indicated that the LCST increased with an increase of acrylamide (AAm) content in the co-polymer composition. The kinetics of the thermosensitice phase transitions of the microgel particles were investigated by time-course UV-vis spectroscopy. The results indicated that the higher the content of AAm in copolymer composition, the more time is required for equilibrium deswelling and the less time required for equilibrium swelling. In addition, the time required for equilibrium deswelling decreased with an increase of the content of the microgel particles in dispersions. By contrast, the time required for equilibrium swelling increased slightly. Thus, a suitable LCST and time required for equilibrium of phase transition can be achieved by adjusting the molar ratio of the comonomers in the microgels and the content of the microgel particles in dispersions. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 321-326, 2009.