2003–04 Celtic League
The 2003–04 Celtic League was the third Celtic League season, and the first following the formation of the five regional rugby sides in Wales. The Celtic League, having previously been played as a pool stage followed by knockout rounds was restructured into a typical league system, based on home and away games only. The league was won by the Llanelli Scarlets, with all the other Welsh regions finishing in the top 6. Following this season, the Celtic Warriors were bought-out and disbanded by the Welsh Rugby Union, and in subsequent years, only four Welsh sides have competed.
Teams
| Team | Stadium | Capacity | City, Area |
 Borders | Netherdale | 6,000 | Galashiels, Scotland |
 Cardiff Blues | Cardiff Arms Park | 12,500 | Cardiff, Wales |
| Celtic Warriors | Brewery Field Sardis Road | 12,000 8,000 | Bridgend, Wales Pontypridd, Wales |
 Connacht | Galway Sportsgrounds | 5,500 | Galway, Republic of Ireland |
| Edinburgh | Meadowbank Stadium | 7,500 | Edinburgh, Scotland |
| Glasgow | Hughenden Stadium | 6,000 | Glasgow, Scotland |
| Leinster | Donnybrook Stadium | 6,000 | Dublin, Republic of Ireland |
| Llanelli Scarlets | Stradey Park | 10,800 | Llanelli, Wales |
| Munster | Thomond Park Musgrave Park | 13,200 8,300 | Limerick, Republic of Ireland Cork, Republic of Ireland |
| Neath-Swansea Ospreys | St Helen's The Gnoll | 4,500 6,000 | Swansea, Wales Neath, Wales |
| Newport Gwent Dragons | Rodney Parade | 12,000 | Newport, Wales |
| Ulster | Ravenhill | 12,800 | Belfast, Northern Ireland |