Keiko Nagaoka (永岡 桂子, Nagaoka Keiko, born December 8, 1953) is a Japanese politician serving in the House of Representatives in the Diet (national legislature) as a member of the Liberal Democratic Party.

In January 1978 she married Yoji Nagaoka, who at that time was a bureaucrat in the Ministry of Agriculture, Forestry and Fisheries.

In 2005, Nagaoka's husband cast a vote in favor the privatization of the Japanese Post Office (which later became the Japan Post Network in 2007), thereby incurring the wrath of Banking Minister Shizuka Kamei, who was the leader of his faction within the LDP.

Although he did not leave a suicide note, stress over political matters was widely cited as the reason.

[2] Following her husband's suicide, Nagaoka announced her candidacy for his seat (Ibaraki District 7) in the 2005 Japanese general election, with the assent of the LDP.