Bipolar membranes are of practical interest in a new process for the commercial production of acids and bases. In this study, the effect of polymer components and structure on membrane potential, rectification and water splitting in bipolar membranes was discussed. The experimental results for the membrane potential agree well with the theoretical predictions if the effective charge densities of bipolar membranes were assumed to be 0.0001 times smaller than those which were estimated for each layer separately. The results of the water splitting and rectification effects show that a membrane exhibiting a high rectification effect has a low water splitting effect. The water splitting ability depends on the thickness of the anion exchange layer. Though it has been pointed out that the state of the intermediate boundary region is also responsible for water splitting, the results indicate that the chemical composition of the anion exchange layer plays an important role. If the membrane structure is similar to an ionomer, the water splitting is also more effective. It is very important to prevent water swelling as far as possible, not only by polymer crosslinking but also by supporting the membrane with woven cloth.