Striker Michael Leddy scored twice in the first-half cancelling out goals from Poland's Marcin Barton as the team went into the break level at 2-2.
Poland took the lead for the third time, seven minutes into the second-half courtesy of a Krzysztof Babs goal before Tomasz Pienko scored from the penalty spot to confirm the 4-2 win.
Speaking after the defeat, Head Coach Jason Donohue was happy with his side's performance over the two games in the Polish town of Police.
"We've given 18 players their international debut, with all of them starting a game for their country. We've educated the players over the past week. It's a huge stepping stone for these players in their career."
Poland: Maciej Styn, Jakub Kolan, Borys Freillich, Mateusz Lipp, Jakub Zlock, Ivo Kaczmarski, Joshua Klockner, Adrian Tyminski, Tomasz Pienko, Marcin Barton, Kacper Duda.
Republic of Ireland: Aaron Mannix; Craig King (Tommy Fogarty 60), Aaron O'Reilly, Darragh Reilly (captain) (Evan Ferguson 60), John Ryan; Luke McGlynn (Glory Nzingo 52), Ben Curtis (Jamie Mullins 60), John Joe Power; Conor Campbell (Sean Fitzpatrick 60), Michael Leddy, Cian Kelly (Ben Quinn 52).