David O'Callaghan, Brian O'Hara and Nevin Spence all come into the squad, benefiting from their performances for the Under-20 Development side in their recent win against France in April, in addition to Jonny Shiels who was capped for Ireland Under-19s last season.
Ireland has been placed in Pool A of the Junior World Championship which is taking place in Japan for the first time.
Their opening three games see them play Argentina, defending champions New Zealand and newcomers to the top tier tournament, Uruguay.
The side will be captained again by number 8 Peter O'Mahony, whose leadership qualities were displayed during the recent RBS U-20 6 Nations.
Commenting on the build-up to the tournament, head coach Allen Clarke said: "We meet up the week prior to our first game against Argentina. Some of the squad will come in on the Friday, those who live outside of Dublin.
"The two days' preparation that we have in Dublin, on the Saturday and Sunday before we travel, is going to be absolutely essential to us, so that we deal with the jetlag - there's a time difference of eight hours.
"We want to be comfortable when we get on the plane on Sunday evening that our bodies are syncing towards Japanese time and that we have done the work on the field in preparation for the Argentinian game."
On the make-up of the squad, he added: "We actually have six players in the squad who are eligible for the Under-20 grade next year again.
"They are out of the Under-20 Development squad, and we believe that that is not only beneficial to next year's squad but beneficial to Irish rugby.
"We're not going over to Japan to make up the numbers. We're going over there to test ourselves as individuals, test ourselves as a team and to build on our performances in the Six Nations and the strengths of those performances.
"We also want to progress as a team and there are particular aspects we've been concentrating on - that in itself tells you something about the team.
"Whilst we won four out of five in the Six Nations, we weren't necessarily satisfied with our performances, even in victory, and we're looking to improve on that."
IRELAND UNDER-20 Squad (2009 IRB Junior World Championship, Japan, June 5-21):
Andrew Burke (Garryowen/Munster)
Shane Gahan (Lansdowne/Leinster)
Matthew Healy (Lansdowne/Leinster)
David Kearney (Lansdowne/Leinster)
Michael Keating (Clontarf/Leinster)
Ian Madigan (Blackrock College/Leinster)
Ian McKinley (UCD/Leinster)
Conor Murray (Garryowen/Munster)
Ronan O'Mahony (Garryowen/Munster)
Eamonn Sheridan (Lansdowne/Leinster)
Jonny Shiels (Queen's University/Ulster)
Nevin Spence (Ballynahinch/Ulster)
Mark Flanagan (UCD/Leinster)
Adam Macklin (Belfast Harlequins/Ulster)
Paddy McAllister (Ballynahinch/Ulster)
Jack McGrath (St. Mary's College/Leinster)
David McGregor (Ballynahinch/Ulster)
Michael Noone (Seapoint/Leinster)
David O'Callaghan (UCC/Munster)
Jack O'Connell (Lansdowne/Leinster)
Brian O'Hara (UL Bohemians/Munster)
Peter O'Mahony (Cork Constitution/Munster) (capt)
Rhys Ruddock (Millfield School/Exiles)
Ciaran Ruddock (Neath/Exiles)
Dominic Ryan (Lansdowne/Leinster)
Thomas Sexton (Old Belvedere/Leinster)
Allen Clarke - Coach
Philip Orr - Team Manager
Nigel Carolan - Assistant Coach
Colin McEntee - Assistant Coach
Emma Gallivan - Physiotherapist
Brian Devitt - Doctor
Philip Morrow - Fitness & Conditioning Coach
Vinny Hammond - Analyst
Regina Flanagan - Masseuse
Martin Joyce - Baggage Master
IRB Junior World Championship Pool A Fixtures (all times are local) -
June 5 - 5pm: Argentina v Ireland, Mizuho Rugby Ground, Nagoya
June 5 - 7pm: New Zealand v Uruguay, Mizuho Rugby Ground, Nagoya
June 9 - 5pm: Argentina v Uruguay, Mizuho Rugby Ground, Nagoya
June 9 - 7pm: Ireland v New Zealand, Mizuho Rugby Ground, Nagoya
June 13 - 1pm: Ireland v Uruguay, Mizuho Rugby Ground, Nagoya
June 13 - 3pm: Argentina v New Zealand, Mizuho Rugby Ground, Nagoya
The tournament website can be found here - www.irb.com/jwc - and IrishRugby.ie will have news, features and match reporters throughout the tournament.