BACKGROUND: Research suggests the use of different forms of therapy as a way of decreasing dropout rates in the treatment of post-traumatic stress disorder (PTSD). The psychotherapies to be assessed in this study are trial-based cognitive therapy (TBCT), mindfulness-based health promotion (MBHP) and positive psychotherapy (PPT). OBJECTIVES: (1) to assess the online efficacy of TBCT compared to MBHP and PPT to reduce the symptoms of PTSD in the context of the Coronavirus Disease 2019 (COVID-19) pandemic; (2) to compare the efficacy of these psychotherapies in improving anxiety, depression, guilt and in promoting well-being; and (3) to describe how professionals perceive online treatment. METHODS: A randomized, multicenter, single-blind clinical trial will be conducted, with three separate arms. An estimated sample of 135 patients will receive either TBCT, MBHP or PPT and will be treated through online, individual, weekly visits, totaling 14 sessions. The primary outcome will be CAPS-5 and secondary outcomes will be HADS and WHO-5. The variables used to mediate these outcomes will be the Trauma-Related Guilt Inventory (TRGI), Negative Core Beliefs Inventory (NCBI) and the California Psychotherapy Alliance Scale (CALPAS-P). EXPECTED RESULTS: PTSD symptoms are expected to be reduced after TBCT, MBHP and PPT. No statistical difference is expected to be found among the three. DISCUSSION: The present study will evaluate and contribute towards the development of new psychotherapeutic options for patients with PTSD. The results of this study will allow the dissemination of new effective and adaptable interventions for patients with PTSD.