| Countries: |  Ireland |
| Champions: | Neath-Swansea Ospreys |
| Count: | 1 |
| Runners-Up: | Munster |
| Matches: | 110 |
| Top Point Scorer: | Gavin Henson (Neath-Swansea Ospreys) (175 points) |
| Top Try Scorer: | Kevin Morgan (Newport Gwent Dragons) (12 tries) |
| Website: | pro14rugby.org |
| Prevseason: | 2003–04 |
| Nextseason: | 2005–06 |
The 2004–05 Celtic League was the fourth Celtic League season, and the second following the introduction of regional rugby in Wales. It involved Irish, Scottish and Welsh rugby union clubs. The restructured Celtic League saw the Welsh regional side the Neath-Swansea Ospreys finish top of the table to take the title.
| Team | Stadium | Capacity | City, Area | |
|---|---|---|---|---|
| Borders | 6,000 | Galashiels, Scotland | ||
| Cardiff Blues | 12,500 | Cardiff, Wales | ||
| Galway Sportsgrounds | 5,500 | Galway, Republic of Ireland | ||
| Edinburgh | 67,800 | Edinburgh, Scotland | ||
| Glasgow Warriors | Hughenden Stadium | 6,000 | Glasgow, Scotland | |
| Donnybrook Stadium | 6,000 | Dublin, Republic of Ireland | ||
| Llanelli Scarlets | Stradey Park | 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 | Neath-Swansea Ospreys | 20 | 16 | 1 | 3 | 508 | 267 | +241 | 53 | 27 | 7 | 3 | 76 | |
| 2 | Munster | 20 | 15 | 1 | 4 | 470 | 331 | +139 | 54 | 33 | 6 | 1 | 69 | |
| 3 | Leinster | 20 | 12 | 1 | 7 | 455 | 350 | +105 | 46 | 32 | 4 | 3 | 57 | |
| 4 | Newport Gwent Dragons | 20 | 11 | 0 | 9 | 381 | 436 | −55 | 39 | 43 | 4 | 2 | 50 | |
| 5 | Llanelli Scarlets | 20 | 9 | 0 | 11 | 402 | 446 | −44 | 48 | 42 | 7 | 3 | 46 | |
| 6 | Glasgow Warriors | 20 | 8 | 1 | 11 | 465 | 466 | −1 | 40 | 58 | 4 | 7 | 45 | |
| 7 | Edinburgh | 20 | 9 | 0 | 11 | 409 | 407 | +2 | 47 | 40 | 4 | 4 | 44 | |
| 8 | Ulster | 20 | 9 | 0 | 11 | 363 | 387 | −24 | 37 | 34 | 2 | 5 | 43 | |
| 9 | Cardiff Blues | 20 | 8 | 1 | 11 | 350 | 404 | −54 | 35 | 41 | 2 | 4 | 40 | |
| 10 | Connacht | 20 | 7 | 1 | 12 | 317 | 407 | −90 | 32 | 46 | 2 | 5 | 37 | |
| 11 | Borders | 20 | 3 | 0 | 17 | 337 | 556 | −219 | 31 | 66 | 2 | 4 | 18 | |
| 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 | 175 | |||
| 2 | 158 | |||
| 3 | 153 | |||
| 5 | 152 |
| Rank | Player | Club | Tries[2] | |
|---|---|---|---|---|
| 1 | Kevin Morgan | Newport Gwent Dragons | 12 | |
| 2 | Tommy Bowe | Ulster | 8 | |
 Christian Cullen | Munster | |||
| Jason Spice | Neath-Swansea Ospreys | |||
| 5 |  Aisea Havili | Llanelli Scarlets | 6 |