East takes on west in the regional RaboDirect Pro12 double-header in the capital.
Last year the Scarlets and Ospreys were triumphant and both are favourites to take the spoils again.
The Scarlets are hunting a win that will put them closer to securing the final qualification spot for next year's Rugby Champions Cup.
The Ospreys need five points to keep the heat on Glasgow and Ulster in the battle for the playoffs.
The Dragons are looking to end a run of five games without a victory that has seen them slide to 10th in the table.
The resurgent Blues bid for a hat-trick of wins following their successes against Ulster and Edinburgh.