In recent years, mobile game market has been rapidly growing. Many online game companies in Taiwan have started to enter into this competitive market. Therefore, how to successfully attract customers has become a critical issues. This study, using the most popular mobile game “Candy Crush Saga” as the experimental task and an electroencephalography to record the player’s brain waves before and after completing a stage of the game, aims to find a pattern of the players’ emotional changes to the game. It is expected that this study would be helpful to game design. The study employed laboratory experiment to test brain asymmetry in emotional processing proposed by Davidson in 1984. The result showed that the subjects, while playing game, had distinguishable power spectrum of alpha-waves in their left and right prefrontal cortex, which was consistent with brain asymmetry theory. Besides, this study showed that the players’ emotions were mostly positive when completing a stage in the game.