The Ospreys, who have lost only once, entertain the Blues at the Talbot Athletic Ground, Aberavon with the winner certain to take their place in the December 30 final at the same venue, whilst reigning champions the Scarlets take on the Dragons at Llandovery.
For the Ospreys's the game is vital in more ways than one - not only will a win seal their place in the final, but it will go some way to avenging the huge defeat suffered at the hands of the Blues when the sides met at Pontypridd earlier in the season - the hosts bagging five tries in a 35-3 victory.
Since then, both sides have beaten the Dragons, but whilst the Ospreys won 6-0 at the Scarlets to maintain their push, the Blues conceded ground by losing at home to the Scarlets.
Five defeats from as many games has left the Dragons out of contention, but if coaches Jason Forster and Gareth Baber can put things right, the Gwent region could play a significant part in deciding who reaches the final.
Mostyn Richards, the Welsh Rugby Union's High Performance manager said, "Just as it was last season, the competition and quality of play in this age group has been immense.
"All four regions have developed during the campaign, but only two of the sides can reach the final. It means that we go into this week's final round with everything to play for."
Blues U18's v Ospreys
20/12/2005 - Aberavon RFC
Ceri Llewelyn, James Egan, Matthew Edwards, Luke Ford, Gareth Jones, James Thomas, Rhys Dyer, Sam Warburton, Dan Franks, John Correlis, Jevon Groves, Matt Gardner, Patrick Palmer, Huw Dowden, Tom Price
Chris John, Rhodri Jenkins, Scott Andrews, Gareth Speers, Chris Holcombe, Gareth Williams, Ben Warburton