Depression-vulnerable college students (with both elevated prior depressive symptoms and low current depressive symptoms) wrote on 3 consecutive days in either an expressive writing or a control condition. As predicted, participants scoring above the median on the suppression scale of the Emotion Regulation Questionnaire (Gross & John, 2003) showed significantly lower depression symptoms at the 6-month assessment when they wrote in the expressive writing versus the control condition. Additional analyses revealed that treatment benefits were mediated by changes in the Brooding but not the Reflection scale of the Ruminative Response Scale (Nolen-Hoeksema & Morrow, 1991). A "booster" writing session predicted to enhance treatment benefits failed to have a significant effect.