Poly(2-chloroethyl vinyl ether-alt-maleic anhydride) can exhibit lower critical solution temperature-type phase behavior reversibly by tuning the solvent composition in mixed solvent of tetrahydrofuran (THF) and hexane. The effect of solvent composition and polymer concentration on cloud point of polymer solution was investigated. The cloud point temperature for high molecular weight polymer was lower than that for lower molecular weight polymer. High resolution 1H NMR spectra in mixed solvent of THF-d 8 and hexane were also measured for comprehending thermoresponsive behavior of polymer solution in molecular level; however, any discontinuous change in the NMR signals around the cloud point could not be recognized.