This randomized study examined whether narrative emotional disclosure improves mindfulness, experiential avoidance, and mental health, and how baseline levels of and changes in mindfulness and experiential avoidance relate to mental health. Participants (N=233) wrote repeated traumatic (experimental condition) or unemotional daily events narratives (control condition). Regression analyses showed neither condition nor gender effects on mental health or experiential avoidance at a 1-month follow-up, although the control condition significantly increased in one component of mindfulness. Decreased experiential avoidance (across conditions) and increased mindfulness (in the experimental condition) significantly predicted improved mental health. Narrative disclosure thus did not improve outcomes measured here. However, increasing mindfulness when writing narratives with traumatic content, and decreasing experiential avoidance regardless of writing content, was associated with improved mental health.