The kinetics of the addition of arenesulfinic acids to 4-substituted 2-nitroethenylarenes was studied by means of UV spectrophotometry. The effect of 4-substituting groups in benzenesulfinic acids, and the change in reactivity of nitroethylene system due to typical electron-donating and electron-withdrawing groups were investigated. The substituent effect on benzenesulfinic acid fits Hammett's equation,p-value at 298 K being - 1.12 (r = 0.987). Kinetic studies were carried out at 288-308 K, and the activating energy and the enthalpy of activation were determined.