The rate constants of hydrolysis of ${alpha}$, N-diphenylnitrone and its derivatives have been determined by UV spectrophotometry from pH 2.0 to 13.5, and a rate equation which can be applied over a wide pH range was obtained. On the basis of rate equation, hydrolysis product, and general base and substituent effects, a plausible mechanism of hydrolysis has been proposed: Below pH 5, the hydrolysis was initiated by the protonation and followed by the addition of water to ${alpha}$-carbon. However, above pH 11, the hydrolysis was proceeded by the addition of hydroxide ion to ${alpha}$-carbon. In the range of pH 5-11, the addition of water to nitrone is rate controlling step.