A series of poly(N-isopropylacrylamide-co-methacrylic acid-co-octadecyl acrylate) (poly(NIPAM-co-MAA-co-ODA)) with different monomer molar ratios was synthesized. Critical micelle concentration (CMC) of the polyelectrolyte solution was determined and the CMC increase with methacrylic acid content in the polyelectrolyte. The phase behaviors of the polyelectrolyte solution were studied, and the effects of various factors on the phase transition were discussed. The experimental results indicate that the lower critical solution temperature and the phase transition pH depend on the monomer molar ratio in the polyelectrolyte. Effect of polyelectrolyte concentration on phase transition pH was studied, and results shown that the phase-transition pH is independent of the polyelectrolyte concentration. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 2089-2097, 2011