Parameters which affect the electrosynthesis of 4,4'-dinitroazobenzene from p-nitroaniline on platinum and PbO2 electrodes were investigated and optimum conditions were determined. Maximum conversion efficiency for electrosynthesis was 95% with a pure beta-PbO2 electrode. It was found that the electrocatalytic activity of a PbO2 electrode depends upon its alpha/beta ratio and its degree of crystallinity. The effects of the added base and water on the conversion efficiency were also elucidated.