Prior studies have shown that facial emotion displays communicate emotional states and interpersonal intentions. This study addressed gender differences in aggression based on the facial emotional cues expressed from a fictional opponent. A modified version of the competitive reaction time task (CRTT) was used to measure aggression. Participants (N = 251), between 18-35 years of age, were randomly assigned to one of the four conditions of the fictional opponents’ facial emotional cue displayed during the CRTT: anger, sadness, neutral, or absence of facial expression. After each trial, participants were asked to report their own feelings and to choose a level of noise to administer to their opponent. Finally, motives for aggression were assessed. Results showed that women were less aggressive than men when receiving emotional cues of sadness and anger from the sender. In contrast, no gender differences occurred when a neutral expression was displayed or in the absence of any expression. In addition, men displayed similar levels of aggression across the four conditions, whereas women were more aggressive in both neutral and no feedback conditions than in the sad and anger conditions. Instrumental motives contributed to explaining the overall gender differences in aggression. These results suggest important moderator and mediator factors of gender differences in aggressive behavior.