Kineties for the reactions of pyridines with 1-anthracenesulfonyl chloride (1-ASC) and 3-phenanthrenesulfonyl chloride (3-PSC) was investigated in methanol as solvent. Structural variation in pyridine followed $Br{o}$ nsted and Hammett relations for both 1-ASC and 3-PSC; the corresponding coefficients, {eta};and;{ ho};at;20^{circ}C$ were 0.55, -3.5 for 1-ASC, and 0.43, -2.6 for 3-PSC respectively. Reactivity-selectivity principle was checked in competition system 1-ASC/3-PSC. As a result, this principle was found to hold at experimental temperatures, whereas to break down over in the range of isoselective temperature ($34.3^{circ}C$). Judging from the above results and activation parameters, we concluded that these reactions proceeded by synchronous $S_n2$ mechanism in rate-determining step.