Rationale: 3,4-Methylenedioxymethamphetamine (MDMA) abuse is a substantial problem in young adults. Due to a high focus on body image in this population, two main factors that may encourage MDMA use are the appetite suppressant and locomotor stimulant effects of this drug. The nucleus accumbens (NAc) is a brain region associated with the regulation of motivated and locomotor behaviours, and recent evidence suggests that NAc 5-HT4 receptors are likely to be involved in the appetite suppressant effect of MDMA. It has not yet been shown whether 5-HT4 receptors of the NAc are involved in the locomotor stimulant effects of MDMA, which may also contribute to a reduction in food intake. Objectives: This study aimed to investigate the effect of local antagonism of serotonin 5-HT4 receptors in the NAc in the appetite suppressant and locomotor stimulant effects of MDMA. Methods: Male hooded Wistar rats underwent surgery for the implantation of bilateral NAc microinjection cannulae under isofluorane anesthesia. Following 5-7 days of recovery, the rats received bilateral microinjections of the 5-HT4 antagonist RS39604 into the NAc immediately prior to either saline or MDMA administration. Food intake, water intake, body weight and locomotor activity were measured. Results: RS39604 significantly increased food intake and increased weight loss in MDMA-treated but not saline-treated rats. Measures of MDMA-induced water intake or locomotor activity were not altered by antagonist administration. Conclusions: These results demonstrate that 5-HT4 receptors in the NAc specifically regulate the appetite suppressant effects of MDMA but not MDMA-induced water intake or locomotor activity.