The vapor phase addition of methanol to iso-butylene was carried out in a differential reactor packed with two types of macroreticular ion exchange resin catalyst, Amberlyst 15 and Amberlyst XN 1010. External mass transfer resistance and macropore diffusion resistance could be neglected over the range studied. The experimental data on the reaction rates could be correlated fairly well with the homogeneous model in which equilibrium distribution effect was considered. Catalytically active -SO₃H groups were diluted by partial replacement with -SO₃Na groups, and from which it was investigated that the reaction rates were nonlinearly dependent on the acid concentration in the resin. The functional groups on the surface of the microparticles seemed to have a lower activity than those within the microparticles.