Diet sessions: 114th (regular session opened in December 1988, to June 22), 115th (extraordinary, August 7 to August 12), 116th (extraordinary, September 28 to December 16), 117th (regular, December 25 to 1990, January 24)
In the 15th regular election for the House of Councillors, Liberal Democrats lose their majority for the first time in party history. In the ensuing "twisted Diet" (nejire kokkai), it must cooperate with the Socialist-led opposition as it does not hold a two-thirds majority in the House of Representatives. The Uno cabinet resigns.
August 8: Reformist Toshiki Kaifu from the small Kōmoto faction is elected LDP president with 279 votes against Yoshirō Hayashi (Nikaidō group, a breakaway group from the Takeshita faction, 120 votes) and Shintarō Ishihara (formerly with his own faction that merged into the Abe faction in 1984, 48 votes)
August 9: First Kaifu cabinet formed and formally appointed one day later.
November 4: Sakamoto family murder - Aum Shinrikyo murders a lawyer, Tsutsumi Sakamoto, as well as his wife, Satoko, and infant son, Tatsuhiko, who had been working on a lawsuit against the religious group.
November 22: The Japan Trade Union Confederation, or "RENGO", is founded with the merger of the Japan Confederation of Labor (Dōmei) and the Federation of Independent Labor Unions (Chūritsu Rōren).