BackgroundElderly population in low- and middle-income countries is rapidly growing, which indicates an increase in the number of dependent people needing long-term care. Caring for the elderly is difficult and stressful and threatens physical and mental health of informal caregivers. We aim to design a web-based support group and assess its effectiveness on depression, anxiety, and stress among elderly informal caregivers.MethodsThis is a protocol for a two-arm randomized controlled trial. A total of 160 informal elderly caregivers will be recruited from the southern area of Tehran. Eligible participants will be randomly allocated to two intervention and control groups. The inclusion criteria include not receiving salary for caring, having primary responsibility for care, having smartphone/tablet/computer, being able to use the contents and web applications, having at least one month of experience in caring for the elderly, and having access to the Internet at least once weekly. The intervention will be implemented by giving an account access to the designed website. Depression, anxiety, and stress will be assessed using the DASS21 questionnaire at baseline, and at the end of third and sixth months.DiscussionOur findings can pave the way for improving the mental health of informal caregivers of the elderly through provision of web-based supportive services. This study stands as an opportunity to address the needs of caregivers and help them support each other in a novel way.Trial registrationIran Randomized Clinical Trial Center IRCT20201012048999N1. Registered on 25 December 2020 (current status: ongoing).The World Health Organization Trial Registration Data Set is in Additional file 1Protocol versionSecond version 2021-05-27