Background: Anxiety is a common symptom in patients with the Acute Coronary Syndrome (ACS), which can threaten their quality of life. This study was done to compare the effects of aromatherapy using lavender and Benson’s relaxation technique on the anxiety of patients with ACS. Methods: In this randomized clinical trial, 96 patients with ACS were selected using consecutive sampling method from two hospitals in an urban area of Iran. The patients were randomly assigned to three groups of aromatherapy (n=32), Benson’s relaxation (n=32), and control (n=32) using the block size of six. The interventions were performed on two consecutive days, once a day for 20 min. Anxiety was measured before and immediately after the intervention using the Spielberger’s Anxiety Inventory. Data were analyzed using the Chi-square test, Fisher’s exact test, one-way Analysis Of Variance (ANOVA), Bonferroni post hoc test, and mixed-model repeated-measures ANOVA with a 3*2*2 design by the SPSS V. 16. Results: There was no statistically significant difference in state and trait anxiety scores between the groups after the intervention on different time points (P> 0.05). The time (P=0.001), group-day interaction (P=0.005), and time (pretest and posttest) and day (P=0.029) effect on state anxiety was statistically significant. The time (P<0.001) and the group-day interaction (P<0.001) effect on trait anxiety was statistically significant. Conclusion: Benson’s relaxation method and lavender aromatherapy did not significantly reduce anxiety in patients with ACS. Considering the anxiety and its complications in patients with ACS and the importance of its management, further studies are needed to determine appropriate care and treatment for these patients and reduce their anxiety.