Nafion tubes that function both as a reaction catalyst and a pervaporation membrane have been used to increase the yield in the esterification of acetic acid with methanol and n-butanol by selectively removing products, mainly water, from the reaction mixture. The experiments were performed at room temperature in a batchwise reactor using acidic protons in Nafion pellets and the Nafion membrane as the reaction catalyst. In some experiments the acidic protons in the membrane were partially or fully exchanged with caesium ions, which increased the intrinsic selectivity of the membrane for water but lowered its permeability. In the methanol reaction, the yield of methyl acetate was increased from the usual equilibrium value of 73% to a maximum of 77%. In the n-butanol reaction,the yield of n-butyl acetate increased from 70% to a maximum of 95%. The effect of the membrane’s catalytic activity on its permselectivity was investigated. The catalytically active membranes showed significantly higher permselectivities for water at the same or higher flux, compared to when no reaction was taking place within the membrane phase.