Disclosed is an on-line role-playing game system and method in which buildings arranged on a road map are developed according to a degree of experience of a user who performs a quest. The method includes the steps of a) by a gamer, accessing an on-line role-playing game server; b) by the gamer, executing the on-line role-playing game; c) by the gamer, performing a quest of the on-line role-playing game; d) updating a degree of experience of the gamer when the gamer accomplishes the quest; and e) developing a building arranged on a road map for the performance of the quest in correspondence with the degree of experience of the gamer. According to the present invention, by applying a building development process to an on-line role-playing game, a limited map for progressing an RPG game story can be efficiently utilized, and, in addition, diverse maps reflecting characteristics of gamers who access the same game for a long time can be provided without imposing a burden on a game server.