The Social Democratic Party (SDP) is a political party of Japan. It was formerly known as the Japan Socialist Party (JSP).

The Social Democratic Party won 6 seats at the general election of November 9, 2003. The SDP obtained 18 seats in the previous elections.

Doi Takako was a leader of the party from 1986, but she resigned in 2003.

Fukushima Mizuho was elected as the new leader of the party on Novenber 15, 2003.

See also: Japan, Japan general election, 2003, Politics of Japan