This study aims to investigate the effectiveness of web-based intervention on social acknowledgement and disclosure of trauma and to examine the mediating effect of the improvement in social acknowledgement and disclosure of trauma on the reduction of posttraumatic stress disorder symptoms. A randomized controlled trial was used, with 21 participants in a web-based intervention group and 29 participants in a wait-list control group completing a pre-test and post-test. Results showed that social acknowledgement and disclosure of trauma improved significantly after 1-month intervention, and this improvement mediated the reduction in the posttraumatic stress disorder symptoms. Implications and limitations of this study are discussed.