Objectives: The family caregivers of patients undergoing coronary artery bypass graft (CABG) surgery experience considerable physical and emotional distress. This study aimed to investigate the effect of an educational support programme on caregiver burden among the family caregivers of patients undergoing CABG surgery in Iran. Methods: This non-randomised controlled clinical trial was conducted from January to April 2017 at a cardiovascular centre in Tehran, Iran. A total of 80 family caregivers of patients undergoing CABG surgery were sequentially selected and non-randomly assigned to intervention and control groups. The control group received routine care, whereas the intervention group received additional education sessions at baseline, prior to surgery, the day after surgery and before discharge. Caregiver burden was compared at baseline and six weeks post-discharge using the Persian-language versions of the Caregiver Burden Inventory (CBI) and Katz Index of Independence in Activities of Daily Living (IADL). Results: A significant difference was observed between family caregivers in the control and intervention groups with regards to pre-post differences in mean CBI scores (+1.67 ± 19.23 versus +17.45 ± 9.83; P <0.001), with an effect size of −1.14. In addition, there was a significant increase in mean post-discharge IADL scores among CABG patients in the intervention group compared to the control group (4.42 ± 1.05 versus 3.07 ± 1.09; P <0.001). Conclusion: An educational support programme significantly reduced caregiver burden among the family members of patients undergoing CABG surgery in Iran. As such, in addition to routine care, healthcare providers should provide educational support to this population to help mitigate caregiver burden. Keywords: Caregiver Burden; Coronary Artery Bypass Surgery; Patient Education as Topic; Caregivers; Education; Quality of Life; Controlled Clinical Trial; Iran.