Previous studies have demonstrated that oxytocin was a viable therapy option for postpartum depression. However, the role remains controversial. To evaluate the efficacy of oxytocin on women postpartum depression, we searched PubMed, Web of Science, Cochrane Library, and EmBase for literatures from inception of the database to April 18th, 2022. Randomized controlled trials (RCTs) that investigated the effects of oxytocin on postpartum depression were selected for this study. Six RCTs (195 women) were gathered. The effects of oxytocin were roughly divided into emotion and cognition. The modulation of oxytocin to women's emotion was demonstrated in four of the trials. The results were conflicting: One trial showed that oxytocin alleviated the depressive mood; two trials showed that oxytocin had no effect (but reduce negative thoughts in healthy mothers, or decrease the narcissistic trait); another trial showed that oxytocin aggravated depression. Women's cognition was shown to be regulated by oxytocin in four of the trials. In general, oxytocin enhanced postpartum depressive women's perception of their relationship with the infants. This systematic review showed that the effect of oxytocin on postpartum depression is still uncertain. We partly support that exogenous oxytocin might improve the cognition of women with postpartum depression to their infants, while the effect on emotion is still controversial. Further RCTs with larger samples and more diversified evaluation criteria are needed to better reveal its efficacy on postpartum depression.