Wales' youngsters dominated long spells of this friendly international at Ninian Park, but failed force the win they deserved.
The hosts created a string of second-half chances, but the Asian champions held out.
Substitute James Collins and David Pipe came closet to breaking the deadlock, but Young-Kwang Kim saved well in the Korean goal.
Wales boss Mark Hughes was there to run the rule over his country's young generation at Ninian Park.
And he would have been impressed with the displays of Coventry pair Pipe and Lee Fowler, as well as Crewe's David Vaughan
Hughes also kept a close eye on Aston Villa's young defender Rob Edwards was very much in the spotlight.
 David Pipe escapes a tackle from Beom-Seok Oh |
He was neat, uncomplicated and reliable at right-back as Wales took on the Koreans who are on a European tour as warm-up for the world under-20 finals in Dubai.
Gil Hoon Lee and Sung Kuk Chol could both have scored early on for the visitors, but Jason Brown was strong and commanding in goal.
Manchester United's Matthew Williams missed arguably the best chance of the match when he miss-hit his shot in the six yard box from Pipe's cross.
Kevin Gall also missed from a good position after excellent work on the right by Michael Brough.
Substitute Gareth Williams went close with a 25-yard shot and a close range stab as Wales dominated the closing stages.
Wales manager Jimmy Shoulder would have been happy with the number of chances created.
A little more composure in front of goal would have brought a very creditable victory against tough opposition.
Wales Under-20: J Brown (Gillingham), R Edwards (Aston Villa), M Price (unattached), S Pejic (Wrexham), R Day (capt, Mansfield), M Brough (Notts County), D Pipe (Coventry), L Fowler (Coventry), K Gall (Yeovil), M Williams (Man Utd), D Vaughan (Crewe)
Subs: M Rees (Milwall), R Evans (Birmingham), A Davies (Southampton), G Williams (C Palace), J Collins (cardiff), P Whitfield (Wrexham).
South Korea Under-20: Kwang-Kim, Hwan Lim, Kyu Kim, Yoon Cho, Seok Oh, Woo Kim, Hoon Lee, Woong Han, Gook Jung, Kuk Chol, Hun Kim.
Subs: Il Sung, Jin Yeo, Lee, Bum Kim, Hoon Baek, Jong Lee, Chul Kim.
Referee: M Whitby (Wales)