This paper sets out to investigate how the basal activation of the parasympathetic and sympathetic nervous systems may affect and predict the decision-making performance of players in serious games. In order to investigate the basal activation of both branches of the autonomic nervous system, pupil diameter and heart rate were recorded during baseline and analyzed in regards to performance scores in the serious game. It was found that the balance between the parasympathetic and sympathetic activation was responsible for beneficial decision-making performance, while lower sympathetic activation was found to be associated with the higher level reached in the game. It is suggested that the balance between the basal activation of both branches of the autonomic nervous system recorded during the baseline may predict the decision-making performance of players on the subsequent tasks in serious games. © 2019 IEEE.