The dimerization of α-methylstyrene (AMS) in the presence of aqueous sulfuric acid catalyst in liquid-liquid (L-L) mode of operation has been studied and the kinetic parameters have been determined. There was no mass transfer limitation in the process and the reaction was found to be intrinsically first-order. The rate constants, activation energy, and product distribution for the L-L mode of operation have been reported. A plausible explanation for the formation of the industrially important dimer in the presence of alcohols has been presented. The data are new and have not been previously reported in the literature. © 2006 American Institute of Chemical Engineers.