The 40-strong Blues squad will then take on Gloucester, Munster and Leicester with the squad being reduced to 32 after the game against the Tigers.
"It's the first game of a big month for the academy boys," said Blues performance manager Richard Hodges. "It's the start of a long fixture list and the game will be a real test against quality opposition."
The Blues are preparing for their first game in the WRU U18 regional competition against Newport Gwent Dragons at the end of August. All 40 members of the initial squad will be given the chance to impress in the four games before the start of the season.
"We'll be finalising our academy and U18 squad at the end of August," added Hodges. "It's a carrot to dangle for some of the boys."
Blues Under 18s (vs Northampton Saints) 15 Jacob Chilcott 14 Richard Singer 13 Tyler Williams 12 Sam Edwards (c) 11 Jack Huntley 10 Sam Withers 9 Chris Brace 8 Tom Samuel 7 Bradley Llewellyn 6 Dafi Sion Davies 5 Rory Bartle 4 Mike Snook 3 Gus MacPherson 2 Liam Belcher 1 Leon Crump
Replacements: Ryan Spriggs, Aiden Luxton, Shane Young, Ollie Hitchins, Rory Harries, Garin Smith, Jarrod Evans.