2008–09 Principality Premiership
| Welsh Premier Division |
| Founded |
| 1995 |
| Nation |
| Relegation To |
| WRU Division One East |
| WRU Division One West |
| Number of Teams |
| 14 |
| Level on Pyramid |
| Level 1 |
| Champions |
| Cardiff RFC |
| Relegated |
| Bridgend Ravens |
| Website |
The 2008–09 Principality Premiership was the fourteenth Principality Premiership season and the fifth under its current format. The season began in September 2008 and ended in May 2009. Fourteen teams played each other on a home and away basis, with teams earning four points for a win, and a bonus point for scoring four or more tries in a match. The losing team may also earn a bonus point if they lose by seven points or less.
The fourteen teams competing were Aberavon RFC, Bedwas RFC, Bridgend Ravens, Cardiff RFC, Cross Keys RFC, Ebbw Vale RFC, Glamorgan Wanderers RFC, Llandovery RFC, Llanelli RFC, Neath RFC, Newport RFC, Pontypool RFC, Pontypridd RFC, Swansea RFC.