Kinetic studies for the nucleophilic substitution reactions of the benzoic anhydrides with anilines in methanol-acetonitrile mixtures at$35.0{circ}C$have been carried out in order to elucidate the reaction mechanism. Individual rate constants$k_{XY}$and$k_{XZ}$were decided from the ratios of the reaction products for the competitive substitution reaction at either one of the two carbonyl carbons in benzoic anhydride. Transition state structure and reaction mechanism were elucidated by the Hammett$p_x,;p_y$and$p_z$values and cross interaction constant$p_x;p_y$and$p_zvalues. The reaction of the benzoic anhydride has been proposed to proceed by a frontside attack$S_N2 $mechanism with four-membered ring transition state from unusually large magnitude of the$ρ_X,;ρ_{XY},;ρ_{XZ}$and positive$p_Y$values.