Emotions are thought to be a key factor that critically influences human decision-making. Emotion regulation can help to mitigate emotion related decision biases and eventually lead to a better decision performance. Serious games emerged as a new angle introducing technological methods to learning emotion regulation, where meaningful biofeedback information displays player's emotional state. This thesis investigates emotions and the effect of emotion regulation on decision performance. Furthermore, it explores design and evaluation methods for creating serious games where emotion regulation can be learned and practiced. The scope of this thesis was limited to serious games for emotion regulation training using psychophysiological methods to communicate user's affective information. Using the psychophysiological methods, emotions and their underlying neural mechanism have been explored. Through design and evaluation of serious games using those methods, effects of emotion regulation have been investigated where decision performance has been measured and analyzed. The proposed metrics for designing and evaluating such affective serious games have been exhaustively evaluated. The research methods used in this thesis were based on both quantitative and qualitative aspects, with true experiment and evaluation research, respectively. Serious games approach to emotion regulation was investigated. The results suggested that two different emotion regulation strategies, suppression and cognitive reappraisal, are optimal for different decision tasks contexts. With careful design methods, valid serious games for training those different strategies could be produced. Moreover, using psychophysiological methods, underlying emotion neural mechanism could be mapped to provide optimal level of arousal for a certain task. The results suggest that it is possible to design and develop serious game applications that provide helpful learning environment where decision makers could practice emotion regulation and subsequently improve their decision making.