We report the hydrothermally enhanced hydrolysis of polyacrylonitrile (PAN) in neutral water, which generates photoluminescent polymers with low unsaturation degrees. Despite the hydrophobic nature of PAN, the product can be dissolved in water at a high concentration (≥100 g/L). The product exhibits complete absence of alkenes or aromatic structures, and photoluminescence originates from newly formed N- and O-containing groups. The presence of both n to π* and π to π* transitions is confirmed by time-dependent density functional theory (TD-DFT) calculations. The efficient transformation of PAN benefits from the enhanced hydrolysis of nitrile groups. While similar reactions have been reported previously under alkaline environments, we demonstrate that efficient hydrolysis can also occur in neutral water under the hydrothermal condition. Two additional methods based on different mechanisms are discussed to demonstrate the simplicity and efficiency of the hydrothermal reaction.