Background: Caring for the disabled elderly can cause compassion fatigue in family caregivers. Improving social interactions in online social networks can reduce compassion fatigue by increasing social support. The aim of the study was to explore the effect of sharing experiences in an online support group on compassion fatigue of family caregivers of the disabled elderly.Methods: The study conducted as a randomized clinical trial with intervention and control groups. A total of 58 family caregivers of the disabled elderly in Mashhad were selected via convenience sampling and assigned to the intervention and control groups using the permuted block technique. The intervention group, in addition to taking part in the first online session individually with the researcher, shared their experiences of the problems caused in their family life due to caring for the elderly in an online support group with other caregivers. The control group participated in the first online session only. Both groups completed a demographic information form, WHO Disability Assessment Schedule (WHODAS-II), and Professional Quality of Life (ProQOL) questionnaire. Measurements were made before and after the intervention. Data analysis was performed using SPSS software (version 24).Results: Compassion fatigue reported by the participants in the intervention group did not change significantly after the intervention compared to before the intervention (p˃0.05). About half of the participants reported a moderate level of compassion fatigue before the intervention.Conclusion: In online support groups, peers can share their care experiences to reduce the negative effects of elderly care by perceiving more social support.Trial Registration number: IRCT20200118046173N1