Purpose: The purpose of this study was to examine the effects of aromatherapy on stress responses, autonomic nervous system (ANS) activity, and blood pressure in patients hospitalized to receive coronary angiography (CAG). Methods: A non-equivalent control group with a pretestposttest design was used. The subjects were patients admitted to the day angiography room to receive CAG at E University Hospital (34 in the experimental group and 30 in the control group). The experimental group treatment was inhalation of the aroma oil blended with lavender, ylang-ylang, and neroli at a ratio of 4:2:1 twice before and after CAG. The measurements of stress index, ANS activity, and blood pressure were performed 5 times as follows: at admission, at pre-CAG after treatment I, at post-CAG, 2 hours after treatment II, and 4 hours after treatment II. The data were analyzed using the Mann-Whitney U Test and repeated-measures analysis of variance. Results: Significant interactions in the high frequency of ANS (F=5.58, p=.005) were observed between group and time. Stress index (z =2.14, p=.016), systolic blood pressure (z =4.14, pqqqlt;.005), and diastolic blood pressure (z =3.28, p=.001) were significantly different between the experimental and control groups after 4 hours of treatment II. Conclusion: The findings showed that aromatherapy was not effective before CAG, but was effective after CAG. Therefore, aromatherapy can be used as a nursing intervention for patients receiving CAG.