The 2018 Rakuten Japan Open Tennis Championships was a men's tennis tournament played on indoor hard courts. It was the 45th edition of the Japan Open, and part of the 500 Series of the 2018 ATP World Tour. It was held at the Musashino Forest Sport Plaza in Tokyo, Japan, from October 1 through October 7, 2018. Unseeded Daniil Medvedev, who entered the main draw as a qualifier, won the singles title.
The following players received wildcards into the singles main draw:
The following player received entry as a special exempt:
The following players received entry from the qualifying draw:
The following pairs received wildcards into the doubles main draw:
The following pair received entry from the qualifying draw: