Compulsive sexual behaviour disorder (CSBD) is a medical condition that can impair social and occupational functioning and lead to severe distress. To date, treatment effectiveness studies of CSBD are under-developed; typically, treatment for CSBD is based on guidelines for substance or other behavioural addictions. Mindfulness-based relapse prevention (MBRP) is an evidence-based treatment for substance addiction aimed at, among other things, reducing craving and negative affect—i.e. processes that are implicated in the maintenance of problematic sexual behaviours. However, to our knowledge no prior research has been published evaluating mindfulness-based intervention (MBI) in the treatment of CSBD, except two clinical case reports. Therefore, the aim of the current pilot study was to examine whether MBRP can lead to clinical improvement in CSBD. Methods: Participants were 13 adult males with a diagnosis of CSBD. Before and after the eight-week MBRP intervention, participants completed a booklet of questionnaires including measurements of porn viewing, masturbation and emotional distress. Results: As expected, we found that after MBRP participants spent significantly less time engaging in problematic pornography use and exhibited a decrease in anxiety, depression and obsessive-compulsive (OC) symptoms. Discussion and Conclusions: The findings indicate that MBRP could be beneficial for CSBD individuals. Further clinical effectiveness studies with bigger sample sizes, delayed post-training measurements and randomised control trial design are warranted. In conclusion, MBRP leads to a decrease in time spent watching porn and a decrease in emotional distress in CSBD patients.