Abstract: The hydrolysis kinetics of vinylsulfone dye,Reactive Brilliant Blue KN-R(C.I.Reactive Blue 19),was studied using reversed-phase ion-pair high performance liquid chromatography(HPLC) under the conditions of varied time, temperature and pH value.After the dyes have converted to vinylsulfone structure,the hydrolysis is a pseudo first-order reaction as long as keeps constant.The velocity of hydrolysis increases with increasing the temperature.In terms of the hydrolysis characteristics,the optimized application conditions for Reactive Brilliant Blue KN-R are as follows: temperature is 50～(70 ℃,) pH value is 8～9,time is 40～(80 min.)