The kinetics of hydrolysis of hydrazonyl bromides $(p-H,;p-CH_3,;p-OCH_3,;p-Br,;p-Cl;&;p-NO_2)$ have been investigated by UV spectrometry in $60{\%}$ dioxane-water at $25^{circ}C$ and a rate equation which can be applied over wide pH range was obtained. Below pH2, the rate of hydrolysis of a series of hydrazonyl bromide is accelerated by electrondonating group (${ ho}$ = -0. 94) whereas at the pH values greater than 4, the ${ ho}$-value is 0.54. The rate equation, solvent-, substituent-and bromide ion-effect on the rate of hydrolysis are rationalized in terms of $S_N1$ and $S_N2$ mechanism: below pH 2, the hydrolysis proceed through $S_N2$, however, above pH 4, the hydrolysis is started by the attack of hydroxide ion and in the range pH 2{sim}$4, these two reactions occur competitively.