Background: Considering the side effects of pharmacological methods, there has been a suggestion to use nonpharmacological methods such Aromatherapy following coronary artery bypass grafting (CABG). This study aims to evaluate the effectiveness of lavender 2% aromatherapy on sternotomy pain intensity after coronary artery bypass graft surgery in patients who have undergone surgery. Materials and Methods: During this clinical trial, 50 patients who were candidates for CABG, were randomly divided into two equal groups, that is, the control group (n = 25) and the case group (n = 25). Following CABG, the case group received two drops of 2% lavender oil every 15 minutes with supplemental oxygen and the control group received only supplemental oxygen through a face mask. The data collection tools comprised of the demographic check list and visual analog scale (VAS) for evaluating the pain intensity. The pain intensity were assessed pre- and five, 30, and 60 minutes post aromatherapy. The final data were analyzed by the t-test and chi-squared test. Results: The findings showed that the pain perception intensity in the case group was lower than that in the control group at the 30- and 60-minute phases after intervention (P < 0.0001). Conclusion: The result indicated that aromatherapy can be used as a complementary method in postoperative pain reduction, as it reduced pain. The patients require two sedative drugs, and moreover, it avoids expenses of treatment.