| Date: | 20 – 26 November (men's) 27 November – 3 December (women's) |
| Edition: | 16th (men's) 6th (women's) |
| Category: | ATP Challenger Tour ITF Women's World Tennis Tour |
| Surface: | Hard |
| Location: | Yokohama, Japan |
| Champms: |  Yosuke Watanuki |
| Champmd: |  Filip Bergevi / Mick Veldheer |
| Champws: | Aliona Falei |
| Champwd: | Liang En-shuo /  Tang Qianhui |
The 2023 Keio Challenger was a professional tennis tournament played on hard courts. It was the 16th (men's) and 6th (women's) editions of the tournament and part of the 2023 ATP Challenger Tour and the 2023 ITF Women's World Tennis Tour. It took place in Yokohama, Japan between 20 November and 3 December 2023.
| Country | Player | Rank1 | Seed | |
|---|---|---|---|---|
| Japan | Yosuke Watanuki | 81 | 1 | |
 Austria | Jurij Rodionov | 107 | 2 | |
 United States | Michael Mmoh | 109 | 3 | |
 Australia | James Duckworth | 113 | 4 | |
| United States | ||||
 Italy | Luca Nardi | 128 | 6 | |
| Australia | Marc Polmans | 158 | 7 | |
| Leandro Riedi | 160 | 8 |
The following players received wildcards into the singles main draw:
The following player received entry into the singles main draw as an alternate:
The following players received entry from the qualifying draw:
The following players received entry as lucky losers:
Chung Yun-seong
Mathys Erhard Giovanni FonioSee main article: article and 2023 Keio Challenger – Men's singles.
Yosuke Watanuki def. Yuta Shimizu 7–6(7–5), 6–4. Ayano Shimizu, 6–3, 7–5See main article: article and 2023 Keio Challenger – Men's doubles.
Filip Bergevi / Mick Veldheer def. Ray Ho / Calum Puttergill 2–6, 7–5, [11–9]. Tang Qianhui def. Aoi Ito / Natsumi Kawaguchi, Walkover
