A game execution method and system of a mobile terminal includes an Internet-based device synchronized with at least one mobile terminal through a game server and receiving a specific game screen that is requested from the mobile terminal from the game server to display. The game server synchronizes the Internet-based device with the at least one mobile terminal and transmits return data with respect to an input signal of manipulating the specific game to the mobile terminal. The mobile terminal downloads and executes game data, transmitting to the game server the input signal of manipulating the specific game, and executes an effect function corresponding to the return data.