Purpose: This study was done to determine the effects of aromatherapy on anxiety and discomfort for patients who were having colonoscopy. Methods: The study used a nonequivalent control group non-synchronized design. The participants were 48 people who were undergoing colonoscopy in a university hospital. The experimental group inhaled a blend of essential oil with neroli, camomile, lavender and lemon through an aroma stone for 5minutes before the examination. Then the aroma stone was put on the side of the pillow to spread the aroma scent in the room. The experimental group could inhale the aroma scent as soon as they came into the room and during the examination process. The control group received only fundamental nursing care. Results: Aromatherapy significantly decreased VAS anxiety. There were also significant differences in facial change and, tone change for objective discomfort. But there were no significant differences in subjective discomfort between the groups nor were there any significant differences in vital signs. Conclusion: Aromatherapy was perceived as an useful intervention to reduce anxiety and objective discomfort of patients receiving colonoscopy. The results of this study could be utilized as a clinical nursing intervention.