The 2017–18 Top League was the 15th season of Japan's top-tier domestic rugby union competition, the Top League. The tournament was won by Suntory Sungoliath for the fifth time, beating Panasonic Wild Knights 12–8 in the final played on 13 January 2018. Kintetsu Liners were automatically relegated to the second-tier Top Challenge League competition for 2018 and NTT DoCoMo Red Hurricanes were also relegated after losing in their relegation play-off match.