Psychology and Economics are two scientific areas who have walked different paths concerning the understanding of human behavior, many times with conflicting results. In this study we analyzed how mood, measured in it’s valence, affects economic behavior. For that we used the Ultimatum Game (UG), an economic decision game, played by Proposers and Receivers, in which concerns about fairness and self interest conflict. The results, although, not statistically significant, indicate that mood is an influence factor in the decisions made in the UG. Proposers in a positive mood show a greater proportion on unfair offers than Proposers in a negative mood, while Receivers in a negative mood are more willing to accept an unfair offer than Receivers in a positive mood. These results are in line with the mood theories that postulate mood as a mediator in the choice of cognitive processing mode, heuristic or systematic, and with the theories that view mood as a signal of the environment, that serves as a regulator of available resources.