AIM: To evaluate the impact of a psychoeducational, mobile health intervention based on cognitive behavioural therapy and mindfulness-based approaches on the mental health of healthcare workers at the frontline against COVID-19 in Spain. DESIGN: We will carry out a two-week, individually randomized, parallel group, controlled trial. Participants will be individually randomized to receive the PsyCovidApp intervention or control App intervention. METHODS: The PsyCovidApp intervention will include five modules: emotional skills, lifestyle behaviour, work stress and burnout, social support, and practical tools. Healthcare workers having attended patients with COVID-19 will be randomized to receive the PsyCovidApp intervention (intervention group) or a control App intervention (control group). A total of 440 healthcare workers will be necessary to assure statistical power. Measures will be collected telephonically by a team of psychologists at baseline and immediately after the 2 weeks intervention period. Measures will include stress, depression and anxiety (DASS-21 questionnaire-primary endpoint), insomnia (ISI), burnout (MBI-HSS), post-traumatic stress disorder (DTS), and self-efficacy (GSE). The study was funded in May 2020, and was ethically approved in June 2020. Trial participants, outcome assessors and data analysts will be blinded to group allocation. DISCUSSION: Despite the increasing use of mobile health interventions to deliver mental health care, this area of research is still on its infancy. This study will help increase the scientific evidence about the effectiveness of this type of intervention on this specific population and context. IMPACT: Despite the lack of solid evidence about their effectiveness, mobile-based health interventions are already being widely implemented because of their low cost and high scalability. The findings from this study will help health services and organizations to make informed decisions in relation to the development and implementation of this type of interventions, allowing them pondering not only their attractive implementability features, but also empirical data about its benefits. CLINICAL TRIAL REGISTRATION: NCT04393818 (ClinicalTrials.gov identifier). APPROVED FUNDING: May 2020.