Objectives : The purpose of this study is to assess the effect of laser acupuncture at $HT_7$ for reducing mental stress using power spectrum analysis of the heart rate variability. Methods : 36 healthy volunteers(control group: 18, treatment group: 18) participated in this study. After instrumentation and 5-minute rest period, 5-minute metal stress by operation was provided. HRV was recorded before and after the mental stress(1st, 2nd HRV). After 2nd HRV recording, the control group rested for 15 minutes without any treatments. Participants in the treatment group received laser acupuncture to $HT_7$ unilaterally and rested for 15minutes. Points were irradiated for 60seconds, and the intensity was 1.8J(output 20%). And then 3rd HRV was recorded. Results : In simple rest group, LF norm showed a significant change after mental stress. In laser acupuncture group, LF norm, HF norm, LF, HF and LF/HF ratio showed a significant change after mental stress. But there were no significant difference between two groups(ANCOVA test, p>0.05). In laser acupuncture group, LF norm, HF norm, HF and LF/HF ratio showed a significant change after laser acupuncture treatment. And there were significant differences between two groups(p<0.05). Conclusions : This study suggests that laser acupuncture at $HT_7$ can regulate and prevent the alternation of autonomic nervous system due to mental stress.