Problem solving is a learning model which includes well-structured problems and ill-structured problem that can be applied any kind of subject. Game provides those problems to players through presenting antagonists.
First of all, NPC antagonists in MMORPG triggers well-structured problem which can give player a chance to apply her knowledge and practice it.
Meanwhile, PC antagonists triggers conflicts berween rrac human which can push players their knowledge of almost everything they have and it has no boundaries.
To give those problems that provided NPC antagonists pedagogic meaning, game system design should be able to mix instructional goal to game itself. And serious MMORPGs should provide players an environment which can give a chance to fight against other players and it will induce ill-structured problems to players.
Key words: Virtual World, MMORPG, Serious Game, Antagnist, PvP