Tōkyō 25th district is a constituency of the House of Representatives in the Diet of Japan. It is located in the westernmost part of Tokyo prefecture. In of 2012, 321,319 eligible voters were registered in the district giving it the highest vote weight in Tokyo – several districts in former Tokyo city in Eastern Tokyo have more than 450,000 voters – but still more than 1.5 times as many voters as the least populated electoral districts in Japan. Before the electoral reform of 1994, the area had been part of that elected five Representatives by single non-transferable vote.