The applied voltage equation and the current density equation are formulated for the electrolysis of the anolyte, aqueous quaternary ammonium chloride, and the catholyte, aqueous quaternary ammonium hydroxide, separated with a cation exchange membrane. The two equations reveal the factors that affect the current efficiency and the voltage efficiency. The effects of the factors on the efficiencies were investigated experimentally. The results show that Nafion 901 is a suitable cation exchange membrane, and both the current efficiency and voltage efficiency increase with the decreasing size of the quaternary ammonium cation, and for the preparation of benzyltriethy-lammonium hydroxide, the current efficiency is well correlated as epsilon (c) = 1.05(I/FC(a)u(c))(-0.16)(I/FC(c)u(0))(0.28), with r(2)=0.96. The voltage efficiency is correlated as epsilon (-1)(nu) - 1 = 3.78 + (-Il/epsilon (0)kappa (m)) + 1.56ln(-Il/epsilon (0)kappa (m)), with r(2)=0.88. (C) 2001 Elsevier Science B.V. All rights reserved.