ABSTRACT: Background:Individuals who were maltreated during childhood are faced with increased risks for developing various psychological symptoms that are particularly resistant to traditional treatments. This pilot study investigated the effects of a mindfulness based behavioral intervention for young adults with a childhood maltreatment history. Methods:This study looked at self-report psychological questionnaires from 20 subjects (5 males) before and after a mindfulness-based behavioral intervention, compared to 18 subjects (6 males) in the waiting list control group (age range 22-29); all subjects experienced mild-to-moderate childhood maltreatment. We analyzed changes in stress, anxiety, depression, mindfulness and self-compassion related to the intervention with linear mixed effects models; we also analyzed the relationships among questionnaire score changes with partial correlation analyses and mediation analysis. Results:Linear mixed effects model analyses revealed significant group by time interaction on stress (p < 0.01), anxiety (p < 0.05), and self-compassion (p < 0.01), with the mindfulness group having significant reduction in stress and anxiety (p < 0.01), and significant increase in mindfulness (p < 0.05) and self-compassion (p < 0.001). Partial correlation analyses showed that among all subjects from both groups, changes in mindfulness positively correlated with changes in self-compassion (r = 0.578, p = 0.001), which negatively correlated with changes in depression (r = -0.374, p = 0.05) and anxiety (r = -0.395, p < 0.05). Changes in self-compassion mediated, in part, the relationship between changes in mindfulness and changes in anxiety (average causal mediation effect = -4.721, p < 0.05). We observed a dose-dependent effect of the treatment, i.e., the number of intervention sessions attended were negatively correlated with changes in stress (r = -0.674, p < 0.01), anxiety (r = -0.580, p < 0.01), and depression (r = -0.544, p < 0.05), after controlling for the individual differences in childhood maltreatment severity. Conclusion:Our results suggest that, to some extent, the mindfulness-based intervention can be helpful for improving self-compassion and psychological health among young adults with a childhood maltreatment history. Clinical Trial Registration:www.ClinicalTrials.gov, identifier NCT02447744.