Poly(vinyl alcohol) (PVA) was cyanoethylated by reaction with acrylonitrile in the presence of sodium hydroxide and quaternary ammonium halide. Quaternary ammonium halide, acting as a phase transfer catalyst, increases the degree of substitution (DS) of PVA. The DS also increased with increasing acrylonitrile concentration. Cyanoethylation of PVA up to 98% can be achieved under optimum conditions. The hydrolysis of P-cyanoethyl ether of PVA (CN-PVA) was studied. The rate of hydrolysis was affected by the sodium hydroxide concentration and the reaction temperature. The rheological properties of aqueous solution of hydrolysis product of CN-PVA were determined at different temperatures, and the flow activation energy was calculated.