| .Y | Yacc Source File | 195 |
| .Y | Subsampled Raw YUV Image | 360 |
| .Y | Amiga Yabba Compressed File | 460 |
| .Y3A | Yu-Gi-Oh! ONLINE 3 Avatar File | 400 |
| .Y3D | Yu-Gi-Oh! ONLINE 3 Deck File | 233 |
| .Y4M | YUV4MPEG2 Video File | 314 |
| .YAB | Yabasic Source Code | 400 |
| .YAL | Arts & Letters Clipart Library | 400 |
| .YAM | Yahoo! Auctions Data | 450 |
| .YAML | YAML Document | 245 |
| .YAODL | PowerFlip 3D Image File | 360 |
| .YBD | YobiDrive Link File | 400 |
| .YBK | Microsoft Encarta Yearbook File | 300 |
| .YBK | YanCEyWare eBook | 275 |
| .YCHAT | Yahoo! Messenger Chat Log | 350 |
| .YCM | Yugioh Card Maker File | 200 |
| .YDC | Yu-Gi-Oh! Card Deck File | 170 |
| .YDK | Yu-Gi-Oh! Deck File | 273 |
| .YDL | PowerFlip YAODL 3D Image File | 333 |
| .YDR | Yu-Gi-Oh! Power of Chaos Replay File | 156 |
| .YDR | YouiDraw Drawing Project | 250 |
| .YDT | Yu-Gi-Oh! Power of Chaos Data File | 233 |
| .YENC | yEnc File | 467 |
| .YFS | YSFLIGHT Mission File | 250 |
| .YGF | Y Graph Format File | 200 |
| .YKA | Yenka Model File | 340 |
| .YKCOL | Locky Ransomware Encrypted File | 267 |
| .YM | Atari ST Audio File | 283 |
| .YMG | Yahoo! Messenger File | 340 |
| .YML | YAML Document | 178 |
| .YML2 | YML Script | 233 |
| .YMP | YaST Metapackage File | 200 |
| .YNC | yEnc Encoded File | 300 |
| .YOG | Outerra Captured Video File | 320 |
| .YOOKOO | Yookoo Player Playlist File | 267 |
| .YPR | BYOB Project File | 157 |
| .YPS | Yahoo! Messenger Data File | 350 |
| .YRCBCK | YRC Backup Archive | 333 |
| .YRCBKM | YRC Bookmarks Archive | 200 |
| .YRCDAT | YRC Software Data Script | 220 |
| .YSP | BYOB Sprite File | 400 |
| .YTD | Grand Theft Auto 5 Texture File | 204 |
| .YTF | Google Picasa Font Cache | 420 |
| .YTT | YouTube Timed Text File | 233 |
| .YUMTX | YUM Transaction File | 333 |
| .YUV | YUV Encoded Image File | 407 |
| .YUV | YUV Video File | 258 |
| .YZ | YAC Compressed File | 267 |
| .YZ1 | Yamazaki ZIPPER File | 350 |