Aim and Objective: This study investigated the effects of social support, parenting stress and maternal self-efficacy on postpartum depression among adolescent mothers in Jordan. Background: Adolescent pregnancy may have serious health, social and economic consequences for young women, families and communities. In Jordan, the incidence of adolescent pregnancy has increased from 5% in 2012 to 15% in 2018. Little attention has been given to postpartum depression among adolescent mothers in Arab and Middle Eastern countries. Method: In a cross-sectional design using convenience sampling, 200 women aged less than 20 years, six to eight weeks postpartum and who could speak and read Arabic were interviewed in a participating health clinic. The interview occurred before or after a woman's scheduled clinic appointment and included socio-demographic data, Edinburgh Postnatal Depression Scale (EPDS), Maternity Social Support Scale (MSSS), Parenting Stress Scale (PSS) and Perceived Self-efficacy Scale (PSES). Data collection took place between December of 2018 and April of 2019. Reporting followed the STROBE guidelines. Results: Results revealed that 28.5% of adolescent mothers had probable postpartum depression. Mothers who reported high social support, high parenting stress, low self-efficacy, financial stress and marital conflict had significantly higher EPDS scores than those who did not report these stressors. Conclusion: Prevalence of postpartum depression reported in this study warrants immediate action on early assessment, detection and intervention. High levels of social support may feel overwhelming for young mothers and contribute to high parenting stress, low maternal self-efficacy and marital conflict. Relevance to clinical practice: Adolescent mothers are at increased risk of PPD compared to mothers over 20 years of age. Perceived quality rather than availability of social support needs to be considered. Young mothers require education and early intervention prevention strategies to better prepared them for motherhood and manage stressors associated with their changing social role.