Abstract: The 4-tert-butyl-2-(α-methylbenzyl ) phenol (t-BAMBP) is used for the separation of Rb and Cs by means of extraction-chromatography. The radiochemical separation procedure of Rb is simple and efficient. Decontamination factor for Cs is more than 10.6, and recovery ratio for Rb is more than 80%. Traditionally, the t-BAMBP was synthesized based on p-tert-butylphenol and styrene as raw material, Lewis acid as catalyst. In order to improve the reactive condition and increase the yield of t-BAMBP, the ionic liquid, chloride-aluminium (Ⅲ) chloride, was used as catalyst. The alkylation had been investigated, and higher conversion was obtained. The effects of catalyst composition and quantity, reaction temperature and time, ration of reactant were studied. The results show that the ionic liquids have better catalytic performance for the title reaction. The optimal synthetical conditions are as follows: in the reaction, the mole fraction of x(AlCl₃) in ionic liquid is 0.67, the mole ratio of ionic liquid is 1∶010 (4-tert-butylphenol/catalyzer), the reaction time is 5 min, the reaction temperature is above 60℃ and the mole ratio of reactants is 1∶1.2 (4-tert-butylphenol/styrene). At the optimum conditions, yield of t-BAMBP is 40.6%.