Substituent effects of substrate and leaving group for the reaction of substituted ${eta}$-phenylethyl arenesulfonates with pyridine were determined conductometrically in acetonitrile at 50∼70$^{circ}$C. The substituent effect in substrate is not so significant than expected, but still the electron donating substituent shows the slight acceleration to give a small negative ${ ho}$ value and Hammett plots show slight curvature on the acting substituents, even though it is not so remarkable than that of benzyl system. These results represent a little bit the favorable bond breaking at the transition state by the electron donating substituents. The effects of leaving group in the arenesulfonates in which the rate constants are decreased by electron donating substituents, while electron withdrawing groups presented the reverse effects. Hammett ${ ho}$ value is significantly smaller than that of p-nitrobenzyl arenesulfonates and thus, the mechanism should be closer to tight $S_N2$ one. Especially 2,5-dichlorobenzenesulfonate was more accelerated than expected at the additivity of substituents. This facts showed that dichlorobenzenesulfonate anion is more stabilized by the great electron withdrawing substituents at transition state.