| Extension | 描述 | 檔案格式 |
|---|
| u | Unreal Tournament File | 3D Files |
| uccapilog | UCC API Log File | 資料檔 |
| udstate | Android Media Finder File | 系統檔案 |
| ufo | PhotoImpact Graphic File | 圖檔 |
| uha | UHARC compressed archive File | 壓縮檔案 |
| uibak | Backup Disk Image File | 磁碟映像檔 |
| uif | MagicISO Disc Image File | 磁碟映像檔 |
| ukx | Unreal Tournament Animation File | 遊戲檔案 |
| umd | Universal Media Disc File | 磁碟映像檔 |
| unknown | Unknown File | Misc Files |
| unl | Garmin Unlock File | 文字檔 |
| uns2 | Ultra Notes Backup file | 備份檔案 |
| upd | Update File | 系統檔案 |
| update | ISAPI Update File | 系統檔案 |
| upg | Firmware Upgrade File | Misc Files |
| upk | Mass Effect Game File | 遊戲檔案 |
| url | Uniform Resource Locator File | 網頁檔案 |
| urls | GetRight Url List File | Misc Files |
| user | Visual Studio User Options File | 設定檔 |
| usr | User Database File | 設定檔 |
| utx | Unreal Engine Texture File | 圖檔 |
| uwl | User Word List File | Misc Files |
| uwl | User Word List File | Misc Files |