The thermochromism of Ni(II) complexes of cresolphthalein dye was studied in pyridine-containing acrylamide copolymers with N-vinyl-pyrrolidone (VP) or N-isopropylacrylamide (IPA). Pendant pyridine moieties in the copolymers affect the sensitivity of color development and stability of color species. A large temperature dependence was obtained in the copolymer 2-acrylamido-N-3-pyridylpropanoamide pyridine with VP and the developed color was stable in copolymer of N-3-pyridylacrylamide with IPA.