BACKGROUND: Anxiety is the one of the most common problems before the surgery. Its prevalence rate ranged from 11 to 80 percent in all the adult patients. Delay in wound healing and increasing use of narcotics and anesthetics are some of the other accompanying problems. Aromatherapy is one of the complementary medicine components. It is applied by special type of oil extracted from aromatic plants for medical objectives. This study aimed to investigate the effects of inhalation aromatherapy on anxiety level in preoperative patients. METHODS: This was a clinical study done on 72 patients candidate for heart and abdominal surgery admitted in Golestan and Imam Khomeini hospitals. The patients were selected according to our study objectives and inclusion criteria. Then, they were divided in two case and control groups. The Spielberger scale was used for evaluating the anxiety level. Twenty minute of inhalation with handkerchief containing lavandula was used in the case group and placebo also (water) in the control group. RESULTS: The average of anxiety level in inhalation aromatherapy group decreased from 51.00 to 38.61 from before to after the intervention. This average in the inhalation group with placebo was 50.67 before the intervention and decreased to 49.53 after the intervention. The results of independent t-test statistically showed a significant difference between the two groups after the intervention. CONCLUSIONS: The findings showed that inhalation aromatherapy was effective on reduction of anxiety level and this method can be applied as a complementary medicine on the clinic.