Background and Aim: Cesarean section is the most common and painful surgical procedure throughout the world. The aim of this research was to evaluate the effect of lavender aromatherapy on the pain level after cesarean section.Materials and Methods: The present study is a double-blind clinical trial conducted on 110 eligible women undergoing cesarean section. The samples were randomly divided into two groups, namely groups A and B. A lavender extract intervention was given to the group A, and a placebo intervention to the group B. Cotton swabs were impregnated with five drops of 100% lavender extract for the intervention group and with five drops of distilled water in the placebo group. It was inserted in their facial oxygen mask and inhaled for three minutes in 4, 8 and 12 hours after the surgery, and then pain score was measured 30 minutes after the intervention. Data were collected using a demographic questionnaire and the visual analog scale. Data analysis was conducted by Wilcoxon’s test and Mann-Whitney’s U-test to compare the severity of pain before and following the intervention in both groups and its variations. Generalized estimating equations (GEE) with an appropriate linear link function were used to examine the effect of lavender on the severity of pain. The significance level was considered 0.05.Results: The severity of pain had a higher level in the lavender group, while pain intensity showed significant distinction between the two groups only on the second (P=0.039) and the third (P=0.011) interventions. Overall, the variations in pain before and after the intervention were similar in the lavender and placebo groups and showed no significant differences.Conclusion: The results of the present study indicated that lavender extract could be effective in the reduction of the pain of cesarean section in the later hours. Hence, lavender extract could be a suitable alternative complementary medicine for the pain of cesarean section. After adjusting for the confounding variables, the multivariate analysis also showed that lavender had no noticeable positive effect on the severity of pain.