ENBackground: The demand for care during the COVID-19 pandemic has affected the mental health of healthcare workers (HCWs), thus increasing the need for psychosocial support services. Internet-based interventions have previously been found to reduce occupational stress. The study aims to test the effects of an Internet-based stress recovery intervention FOREST among HCWs. Methods: A randomized controlled trial (RCT) parallel group design with three measurement points will be conducted to assess the efficacy of an Internet-based stress recovery intervention FOREST for nurses. The FOREST intervention is a 6-week Internet-based CBT and mindfulness-based program which comprises of six modules: (1) Introduction, (2) Detachment (relaxation and sleep), (3) Distancing, (4) Mastery (challenge), (5) Control, and (6) Keeping the change alive. We will compare the intervention against a waiting list group at pre-test, post-test, and follow-up. Stress recovery, PTSD, complex PTSD, moral injury, the level of stress, depression, anxiety, and psychological well-being will be measured. Discussion: The study will contribute to the development of mental healthcare programs for the HCWs. Based on the outcomes of the study, the FOREST intervention can be further developed or offered to healthcare staff as a tool to cope with occupational stress. Trial registration: ClinicalTrials.gov NCT04817995. Registered on 30 March 2021 Keywords: Internet-based intervention, Stress recovery, PTSD, Moral injury, Healthcare staff. [From the publication]