While various VOCs are known to show neurotoxic effects, the detailed mechanisms of VOCs on autonomic nervous system have not been fully understood partly because objective and quantitative measures to indicate neural abnormalities are still under development. Nevertheless, heart rate variability (HRV) has been recently proposed as an indicative measure of the autonomic defect. In this study, we used HRV as an indicative measure of the autonomic defect to relate their values to the personal concentrations of VOCs measured by a real-time VOC monitor. The measurements were conducted to 7 healthy subjects for 24 hours. The results showed HF powers were decreased for 6 subjects when the TVOC concentration changes were high, indicating the suppression of parasympathetic nervous induced by the exposure to VOCs. The present study indicated these real-time monitoring was useful to characterize the trends of VOC exposures and their effects on autonomic nervous system. Application of the present method is expected to lead to diagnosis and cure for the patients such as MCS and sick building syndrome in the future.