OBJECTIVE: To determine the effectiveness and safety of essential oil from Citrus aurantium on anxiety in patients undergoing coronary angiography. METHODS: A single-blind, randomized controlled trial was conducted in 80 patients experiencing coronary angiography in Imam Ali Hospital in Kermanshah, Iran from April to November in 2016. All patients were randomly divided into intervention and control groups by a random number table, 40 cases in each group. The patients in the intervention group inhaled Citrus aurantium essential oil for 15-20 min about 60 min before angiography. Following the same procedure, distilled water was used instead of Citrus aurantium in the control group. Spielbergers State-Trait Anxiety Inventory (STAI) was filled in and vital signs including systolic blood pressure (SBP), diastolic blood pressure (DBP), respiratory and pulse rate were recorded before and 20 min after the intervention. Adverse reactions after intervention were observed. RESULTS: In the intervention group, the mean scores of STAI, SBP, DBP, respiratory and pulse rate were 53.30 ± 10.13, 134.82 ± 11.75 mm Hg, 84.49 ± 6.99 mm Hg, 17.87 ± 1.73 times/min, and 76.48 ± 12.55 beats/min at baseline and significantly decreased to 42.37 ± 10.15, 124.49 ± 10.48 mm Hg, 79.23 ± 6.62 mm Hg, 14.54 ± 1.43 times/min, and 70.03 ± 13.66 beats/min respectively 20 min after intervention (all P<0.05); however, in the control group, neither anxiety scores nor vital signs changed significantly (P>0.05). All subjects reported no adverse reactions. CONCLUSION: Inhalation of the essential oil from Citrus aurantium was effective in reducing anxiety and stress levels in patients undergoing coronary angiography. TRIAL REGISTRATION IRCT2016040816797N2 (retrospectively registered on 21 April 2016, https://en.irct.ir/trial/15600 ).