12 File Extensions starting with U
| .UDI | Universal Disk Image |
| .UOF | Unified Office Format Document |
| .UOF | Unified Office Format Spreadsheet |
| .UOF | Unified Office Format Presentation |
| .UOP | Unified Office Format Presentation |
| .UOS | Unified Office Format Spreadsheet |
| .UOT | Unified Office Format Document |
| .UPI | Ulead PhotoImpact Image |
| .URT | Utah raster Image |
| .UU | Uuencoded File |
| .UUE | Uuencoded File |
| .UYVY | YUV 16Bits Image |