The purpose of this study is to explore the effects of Chamaecyparis obtusa essential oil on the activity of autonomic nervous system. Heart rate variability (HRV), as an indicator of autonomic nervous system activity and blood pressure were measured before and after inhalation of Chamaecyparis obtusa essential oil. The systolic blood pressure was decreased by inhalation of Chamaecyparis obtusa essential oil (p<0.05). The diastolic blood pressure was not changed significantly by Chamaecyparis obtusa. High frequency (HF) power level was not changed but High frequency/Low frequency (HF/LF) ratio was decreased by Chamaecyparis obtusa essential oil (p<0.05), meaning that parasympathetic nervous system activity was not affected but sympathetic nervous system activity was decreased. These results indicate that Chamaecyparis obtusa essential oil has a modulatory effect on the autonomic nervous system activity.