Indirect anodic oxidation of soyasapogenol B (3β, 22β, 24-trihydroxyolean-12-ene) was carried out using KI as a mediator in t-BuOH-H2O solution, so that the 3-ketone derivative was obtained as the only oxidation product in a favorable yield. As a result of application to various polyhydroxylated triterpenes, selective electrochemical oxidation was shown to occur in the C-3 hydroxyl group of the polyhydroxyl triterpenes with the C-24 hydroxyl group. The reaction pathway is discussed.