In online game, Game-bot is a kind of AI based software which performs laborious tasks for a game-player to accumulate resources such as experience, in-game items. The game-bot causes serious problems of balancing and other game-players’ play in the game. So, detecting and avoiding game-bot’s behaviors in online game is one of the important issues in live game management. This paper proposes a study on a player reaction in MMORPG environment focused on two games of 「TERA」 and 「Knight Online」. We first characterize core game-elements to affect a player’s reaction in game environment change and finally propose a template of a player’s reaction in the game environment change. The paper will contribute to detect a behavior of a game-bot in online-game, effectively.