Objectives : The purpose of this study is to show the differences of mental stress measured with heart rate variability (HRV) and to evaluate the effects of Aromatherapy under mental stress, according to the depression index. Methods : The volunteers were allocated into 2 groups by BDI scores. Each group is divided into 2 subgroups again. After instrumentation and 10-minutes rest period, mental stress by operation was provided for 15-minutes. HRV was recorded before and after the mental stress. Then the control groups rested for 15-minutes. The experimental groups were treated with Aromatherapy. And then HRV was recorded. Results : 1. There were no significant differences in the mean HRT and SDNN between each group. 2. LF, HF, and LF norm showed different changes in each group. 3. LF/HF ratio showed significant changes. Conclusions : These results suggest that psychic factor makes an important rule under the mental stress and the effect of Aromatherapy, and Aromatherapy is effective to recover mental stress.