| Countries: |  Ireland |
| Champions: | Llanelli Scarlets |
| Count: | 1 |
| Runners-Up: | Ulster |
| Matches: | 132 |
| Top Point Scorer: | Neil Jenkins (Celtic Warriors) (273 points) |
| Top Try Scorer: | Jamie Robinson (Cardiff Blues) (12 tries) |
| Website: | www.rabodirectpro12.com |
| Prevseason: | 2002–03 |
| Nextseason: | 2004–05 |
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.
| Team | Stadium | Capacity | City, Area | |
|---|---|---|---|---|
| Borders | 6,000 | Galashiels, Scotland | ||
| Cardiff Blues | 12,500 | Cardiff, Wales | ||
| Celtic Warriors | Brewery Field Sardis Road | 12,000 8,000 | Bridgend, Wales Pontypridd, Wales | |
| Galway Sportsgrounds | 5,500 | Galway, Republic of Ireland | ||
| Edinburgh | Meadowbank Stadium | 7,500 | Edinburgh, Scotland | |
| Glasgow | 6,000 | Glasgow, Scotland | ||
| Donnybrook Stadium | 6,000 | Dublin, Republic of Ireland | ||
| Llanelli Scarlets | 10,800 | Llanelli, Wales | ||
| 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 | 12,000 | Newport, Wales | ||
| 12,800 | Belfast, Northern Ireland |
| Pos | Team | Pld | W | D | L | PF | PA | PD | TF | TA | TBP | LBP | Pts | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | Llanelli Scarlets | 22 | 16 | 1 | 5 | 597 | 385 | +212 | 57 | 39 | 7 | 3 | 76 | |
| 2 | Ulster | 22 | 15 | 0 | 7 | 617 | 363 | +254 | 67 | 29 | 8 | 4 | 72 | |
| 3 | Newport Gwent Dragons | 22 | 16 | 0 | 6 | 590 | 449 | +141 | 59 | 41 | 7 | 1 | 72 | |
| 4 | Celtic Warriors | 22 | 14 | 0 | 8 | 560 | 451 | +109 | 48 | 37 | 5 | 4 | 65 | |
| 5 | Neath–Swansea Ospreys | 22 | 11 | 1 | 10 | 582 | 512 | +70 | 55 | 60 | 5 | 4 | 55 | |
| 6 | Cardiff Blues | 22 | 11 | 0 | 11 | 570 | 467 | +103 | 73 | 54 | 7 | 3 | 54 | |
| 7 | Munster | 22 | 10 | 0 | 12 | 422 | 456 | -34 | 45 | 49 | 6 | 5 | 51 | |
| 8 | Leinster | 22 | 9 | 1 | 12 | 523 | 580 | -57 | 51 | 65 | 4 | 5 | 47 | |
| 9 | Connacht | 22 | 8 | 2 | 12 | 479 | 550 | -71 | 50 | 59 | 5 | 3 | 44 | |
| 10 | Edinburgh | 22 | 9 | 0 | 13 | 454 | 622 | -168 | 52 | 69 | 6 | 2 | 44 | |
| 11 | Glasgow | 22 | 6 | 1 | 15 | 442 | 614 | -172 | 52 | 61 | 3 | 3 | 32 | |
| 12 | Borders | 22 | 4 | 0 | 18 | 363 | 750 | -387 | 42 | 88 | 1 | 5 | 22 | |
Under the standard bonus point system, points are awarded as follows:
| ||||||||||||||
| Source: RaboDirect PRO12 | ||||||||||||||
Note: Flags to the left of player names indicate national team as has been defined under IRB eligibility rules, or primary nationality for players who have not yet earned international senior caps. Players may hold one or more non-IRB nationalities.
| Rank | Player | Club | Points[1] | |
|---|---|---|---|---|
| 1 | Neil Jenkins | Celtic Warriors | 273 | |
| 2 | Gavin Henson | Neath–Swansea Ospreys | 265 | |
| 3 | Gareth Bowen | Llanelli Scarlets | 240 | |
| 4 | Brian O'Meara | Leinster | 195 | |
| 5 | Percy Montgomery | Newport Gwent Dragons | 191 |
| Rank | Player | Club | Tries[2] |
|---|---|---|---|
| 1 | Jamie Robinson | Cardiff Blues | 12 |
| 2 | Conor McPhillips | Connacht | 11 |
| 3 | Jason Forster | Newport Gwent Dragons | 9 |
| Tyrone Howe | Ulster | ||
| Sean Lamont | Glasgow |