Research examining moral decision making has found that stress increases altruistic decisions. Further, it has been shown that psychopathic personality traits are inversely associated with altruistic decisions, while also being associated with blunted stress responses. The present study examined whether psychopathic personality traits moderate the relationship between stress and moral decision making in a healthy undergraduate sample. To manipulate stress, participants were exposed to the Trier Social Stress Test (TSST) or its low stress equivalent. Psychopathic traits were assessed using the Levenson Self-Report Psychopathy Scale (LSRP), autonomic (heart rate, blood pressure), endocrine (cortisol), and subjective stress (STAI-state) were measured throughout the session, and moral decision making was examined using the Everyday Moral Reasoning Task (EMRT). The moderated regression model examining cortisol change was significant, but the models for the other stress measures were not. Those with high psychopathic traits and large cortisol increases gave the fewest altruistic responses, while those with low cortisol increases and low psychopathic traits gave the most altruistic responses; this relationship appeared to be driven by the high stress group. It was expected that psychopathic personality traits would be associated with fewer altruistic decisions, but the finding that larger increases in cortisol were associated with fewer altruistic decisions contradicts the existing literature.