PROBLEM: Low prenatal well-being has adverse outcomes for mother and infant but few interventions currently exist to promote and maintain prenatal well-being. BACKGROUND: Mindfulness and gratitude based interventions consistently demonstrate benefits in diverse populations. Interventions integrating these constructs have potential to improve psychological and physiological health during pregnancy. AIM: The aim of this pilot study is to examine the effect of a novel gratitude and mindfulness based intervention on prenatal stress, cortisol levels, and well-being. METHODS: A pilot randomised controlled trial was conducted with 46 pregnant women. Participants used an online mindfulness and gratitude intervention 4 times a week for 3 weeks. Measures of prenatal stress, salivary cortisol, gratitude, mindfulness, and satisfaction with life were completed at baseline, 1.5 weeks later, and 3 weeks later. FINDINGS: Intervention participants demonstrated significant reductions in prenatal stress in comparison to the control condition (p=.04). Within subjects reductions in waking (p=.004) and evening cortisol (p>.001) measures were observed for intervention participants. Significant effects were not observed for other well-being outcomes. DISCUSSION: Reducing self-report and physiological stress in pregnancy can improve maternal and infant outcomes. The findings of this pilot study indicate potential direct effects of the intervention on self-reported stress in comparison to a treatment-as-usual control. Effects on a biomarker of stress, cortisol, were also observed within the intervention group. CONCLUSION: A brief mindfulness and gratitude based intervention has the potential to reduce stress in pregnancy. Future research is needed to further explore mechanisms and potential benefits of such interventions.