Research on women during the postpartum period has focused primarily on depression, to the exclusion of other aspects of wellbeing and distress. Though research has also described the barriers to getting help with experiences of postpartum emotional distress there is little research on easily accessible and affordable prevention and treatment interventions or consideration of how women’s individual differences may influence the effectiveness of interventions intended to prevent and treat symptoms of emotional distress. In the present study, self-report data was gathered from 257 women at five points in time during the extended postpartum period. Baseline measures of anxiety, depression, wellbeing, and two facets of mindfulness (nonreactivity and nonjudgment of inner experiences) were examined as potential predictors of how two types of positive expressive writing interventions, based on self-affirmation and mindfulness theories, would impact women’s symptoms of depression, anxiety, and complaints related to physical and psychological wellbeing. These conditions were also compared to a waitlist control condition. Contrary to what was hypothesized, there were no significant differences between the writing and waitlist conditions on outcome anxiety, depression, or wellbeing. Additionally, nonjudgment and nonreactivity did not interact with type of writing condition in predicted ways. Compared to the self-affirmation condition, those in the mindfulness condition used more emotion words in their writings, and reported more changes in affect over the course of their individual writing sessions. Post-hoc analyses indicated post-writing negative affect might mediate the relationship between baseline and follow-up depression and anxiety. Limitations and implications of the findings are discussed along with recommendations for future study.