Incumbent Prime Minister Junichiro Koizumi and the Liberal Democratic Party won the most seats in the House of Representatives but failed to secure a majority.

The main opposition Democratic Party made considerable gains, winning 177 of the 480 seats in the House of Representatives, its largest share ever.

On October 11, 2003, following his re-election as leader of the Liberal Democratic Party on September 20, Prime Minister Junichiro Koizumi dissolved the House of Representatives of Japan's Diet.

This action was in accordance with Article 7 of the Constitution of Japan, which grants the Prime Minister the authority to dissolve the lower house after consulting the Emperor.

The LDP continued to enjoy robust support in rural regions and among the elderly, largely due to substantial agricultural subsidies, while the DPJ was more popular with younger voters and in urban centers.

The preceding general election for the Lower House occurred in June 2000 under the leadership of Prime Minister Yoshiro Mori.