Koji Yamasaki (baseball) should not be confused with Koji Yamasaki (field hockey).
| Koji Yamasaki | |
| Position: | Infielder |
| Birth Date: | 31 October 1980 |
| Birth Place: | Yodogawa-ku, Osaka, Japan |
| Bats: | Right |
| Throws: | Right |
| Debutleague: | NPB |
| Debutdate: | October 7 |
| Debutyear: | 2003 |
| Debutteam: | Osaka Kintetsu Buffaloes |
| Statyear: | 2015 season |
| Statleague: | NPB |
| Stat1label: | Batting average |
| Stat1value: | .222 |
| Stat2label: | Home runs |
| Stat2value: | 8 |
| Stat3label: | RBI |
| Stat3value: | 79 |
| Teams: | |
Koji Yamasaki (山﨑 浩司, born October 31, 1980) is a Japanese professional baseball infielder for the Tohoku Rakuten Golden Eagles in Japan's Nippon Professional Baseball.