Three experiments were designed to investigate effects of mood on college students' capacities of moral reasoning. Following a mood induction, the standard or a modified version of the Defining Issues Test (DIT) was administered to measure moral reasoning. The results of Experiment 1, using the standard short form of the DIT, showed elated subjects performed more poorly and took longer than subjects in neutral and sad mood conditions. The results of Experiment 2, using the self-orientated DIT, showed that mildly depressed subjects performed better than did subjects in neutral and happy mood conditions. The results of the third experiment, presenting more socially disturbing moral dilemmas, showed no effect for either happy or sad mood conditions. Reviewing recent literature of studies on mood and cognition, this study extended the theories and predictions of those studies to the moral context for the purpose of exploring our moral reasoning capacities in real life and enriching our current understanding from moral educational situations.