The 2018 Keio Challenger was a professional tennis tournament played on hard courts. It was the thirteenth (ATP) and second (ITF) editions of the tournament and part of the 2018 ATP Challenger Tour and the 2018 ITF Women's Circuit. It took place in Yokohama, Japan between 26 February and 4 March 2018 for the men's edition and between 5 and 11 March 2018 for the women's.
Men's singles main-draw entrants
Seeds
1 Rankings are as of 19 February 2018.
Other entrants
The following players received wildcards into the singles main draw: Shinji Hazawa Kaito Itsusaki Kaito Uesugi Yosuke Watanuki
The following player received entry into the singles main draw as a special exempt: Blake Ellis
The following players received entry from the qualifying draw: Chung Yun-seong Hiroyasu Ehara Hiroki Moriya Jumpei Yamasaki
The following player received entry as a lucky loser: Daniel Nguyen
Women's singles main-draw entrants
Seeds
1 Rankings are as of 26 February 2018.
Other entrants
The following players received wildcards into the singles main draw: Ayumi Hirata Marina Kurosu Megumi Nishimoto Satoko Sueno
The following players received entry from the qualifying draw: Harriet Dart Misa Eguchi Mai Hontama Momoko Kobori Lee Ya-hsuan Ma Yexin Katherine Sebov Moyuka Uchijima
Champions
Men's singles
Yasutaka Uchiyama def. Tatsuma Ito 2–6, 6–3, 6–4.
Women's singles
Veronika Kudermetova def. Harriet Dart, 6–2, 6–4
Men's doubles
Tobias Kamke / Tim Pütz def. Sanchai Ratiwatana / Sonchat Ratiwatana 3–6, 7–5, [12–10].
Women's doubles
Laura Robson / Fanny Stollár def. Momoko Kobori / Chihiro Muramatsu, 5–7, 6–2, [10–4]