Ishii was returned to the House of Representatives in the July 1986 general election, gaining the most votes in the Hyogo 1st district and regaining his seat from Nagae. Upon returning to the House he served three consecutive terms as one of five members for the Hyogo 1st district; he retained his seat at the July 1993 general election after leaving the Liberal Democractic Party and joining the Japan Renewal Party earlier that year. 1994 electoral reforms abolished the multi-member districts and replaced them with smaller single-member districts. In the same year the Renewal Party merged with other parties to form the New Frontier Party. Ishii won the first election in the new Hyogo 1st district at the October 1996 general election as a member of the Frontier Party. In 1998 he joined the short-lived Kokumin no Koe ("People's Voice") and Good Governance parties, which merged into the Democratic Party of Japan. Ishii retained the Hyogo 1st district seat at the June 2000 general election as a DPJ candidate. At the November 2003 general election Ishii was defeated by the LDP's Keisuke Sunada, the younger cousin of Shigetami Sunada with whom Ishii served five of his terms as representative of the old Hyogo 1st district. Despite the loss Ishii was able to retain a seat in the House as a member for the Kinki proportional representation block. At the September 2005 general election Ishii lost to the LDP's Masahito Moriyama and was also unsuccessful in gaining a PR seat. Ishii contested the July 2007 election for the House of Councillors, winning one of 48 seats in the national proportional representation block. He served one term before losing his seat in the July 2013 election.