The activation parameters for the nucleophilic addition reactions of n-propyl-, n-butyl-, n-amyl-and n-hexyl-mercaptan to 3, 4-methylene-dioxy-${eta}$-nitrostyrene were determined at pH 5.8 and pH 2.0, and also the isokinetic temperature of the reactions at pH 5.8 was obtained numerically 262${circ}$K, and at pH 2.0, 17.1${circ}$K. From the values obtained above, the fact that the mercaptan having the longer carbon chain has the greater nucleophilicity of it in the addition reactions has been discussed by the extrathermodynamic analysis of ${Delta}H^{ eq}$and ${Delta}S^{ eq}$.