The effects of inhalation of various concentrations of lavender oil on the excitability of spinal motor neurons were studied by F-wave analysis. Excitability was significantly suppressed after 10 min of inhalation of the 10% concentration. To clarify the underlying mechanism, effects on the autonomic nervous system were studied by analysis of mean heart rate and its variability, by F-waves, after 5 min of 10% concentration inhalation. Heart rate variability results suggest that lavender essential oil influences spinal motor neurons via effects on parasympathetic nerves.