Nucleophilic substitution reactions between Alkanesulfonylchlorides and p-substituted anilines in methanol-acetonitrile mixture have been studied kinetically. Reactivities of substrates, substituent effects of nucleophile and solvent effects indicate that the studied reaction proceeds via <TEX>$S_N2$<TEX>. The kinetic results show that transition state of the reaction between i-PSC and anilines becomes looser as the composition of methanol increases.