| Ugly | 1892 | Pot 8 o's系 |
| Ultimus | 1916 | Himyar系 |
| Umidwar | 1931 | Blandford系 |
| Unbreakable | 1935 | Sickle系 |
| Unbridled | 1987 | Mr. Prospector系 |
| Unbridled's Song | 1993 | Mr. Prospector系 |
| Uncle Mac | 1894 | King Fergus系 |
| Under Fire | 1916 | Swynford系 |
| Underwood | 1944 | Bois Roussel系 |
| Unfuwain | 1985 | Northern Dancer系 |
| Upper Case | 1969 | Princequillo系 |
| Utrillo | 1958 | Dante系 |