Okayama International Circuit (岡山国際サーキット), formerly known as TI Circuit Aida (TIサーキット英田) before 2005, is a 3.7-kilometre (2.3 mi) private motorsport race track in Mimasaka, Okayama Prefecture, Japan. TI was the abbreviation of "Tanaka International" after the name of the golf club owner, Hajime Tanaka, though the name of the circuit was officially "TI Circuit Aida".
As well as hosting racing events, the circuit has rental facilities including bikes and go karts available.
In 1994 and 1995, the TI Circuit hosted the Formula One Pacific Grand Prix; both events were won by Michael Schumacher in his early title-winning years. This race made Japan one of only nine countries to ever host more than one Formula One event in the same year (Autopolis was planned to host a second Japanese race in 1993, but it never came to fruition). It was discontinued primarily due to its location in a remote area of the country. The event was also planned to host a race of the 1996 International Touring Car Championship season in August to replace the F1 race, but the race was instead moved to Suzuka Circuit, held in November.
In 1999, defending JGTC GT300 champion Shingo Tachi was killed when he tested a GT500 Toyota Supra after he suffered from a technical failure that prevented him from slowing down for the first turn. Although no JGTC or Super GT driver have died during their race events so far, the incident occurred almost a year after Tetsuya Ota's near-fatal, fiery accident at Fuji Speedway.
In March 2003, the Tanaka International Company, parent company of the official circuit owner TI Circuit Company, applied for civil rehabilitation. After the application, Unimat Holding Co., Ltd.  announced that it would financially support the TI Circuit Company in keeping the facility open. The company was renamed Okayama International Circuit Co., Ltd. on May 1, 2004, and the circuit was renamed Okayama International Circuit on January 1, 2005.
On October 26, 2008, the circuit hosted a round of the Formula V6 Asia and FIA World Touring Car Championship. The WTCC race was the first FIA world championship race since 1995. However, it was announced on June 21, 2010 that Suzuka Circuit would host the Japan round of the 2011 WTCC season instead of the Okayama International Circuit.
On March 3, 2012, Unimat sold the circuit to Aska Corporation, an auto parts manufacturing company.
In 2018, 12-year-old Juju Noda set the lap record for Formula 4 machinery around the Okayama International Circuit, recording a time of 1 minute 32.8 seconds – nearly a second faster than the previous best time.
- 株式会社岡山国際サーキットの株式取得（子会社化）についてのお知らせ [We resolved on the acquiation of whole stock in Okayama International Circuit Co., Ltd.] (PDF) (Press release) (in Japanese). Aska Corporation. March 12, 2012. Archived from the original (PDF) on September 21, 2013. Retrieved April 24, 2012.
- "Course guide" (in Japanese). Okayama International Circuit website. Retrieved 2012-12-28.
- Cooper, Adam (April 17, 2020). "Why Japan's second F1 race didn't take off". Motorsport.com. Retrieved October 28, 2020.
- O'Connell, R.J. "Remembering Shingo Tachi, 20 Years Later". Dailysportscar. Retrieved 19 October 2020.
- "FIA WTCC TO RACE AT SUZUKA IN 2011". fiawtcc.com. 2010-06-21. Retrieved 2010-07-20.