In this article, we describe the poly(N-isopropylacrylamide)-based thermoresponsive behaviors of fluorescent organic nanocrystals. Aqueous dispersions of thermoresponsive fluorescent nanocrystals were prepared by the reprecipitation method. Fluorescent dyes used for these nanocrystals were perylene, quinacridone, and zinc phthalocyanine. The perylene nanocrystals in the aqueous system using poly(Nisopropylacrylamide) exhibited a significantly increased fluorescence intensity assigned to the emission of the perylene monomer above the cloud point (̃35 °C). Significantly increased fluorescence intensities of quinacridone nanocrystals and zinc phthalocyanine nanocrystals were also observed above the cloud point (̃35 °C). These unique fluorescence behaviors were only observed in the aqueous system using poly(Nisopropylacrylamide).