Objectives: To clarify the effects of lavender oil aroma on the excitatory state of spinal motor neurons, we performed F-wave measurements, which is an index for testing muscle tonus. Methods: The subjects were 19 healthy volunteers (7 males and 3 females for experimental group; average age, 25.9 ± 6.0 years, and 6 males and 3 females for control group; average age 29.1 ± 8.8 years) without any olfactory function disorder. All subjects had no prior experience with aromatherapy. F-waves were measured before and after inhalation of lavender oil in a supine position. The objective nerve was median nerve, and F-waves were elicited by supramaximal stimulation at left thenar eminence. After measurements, we asked the subjects whether they liked the smell of lavender. Results: The amplitude of the measured F-waves was significantly smaller at 5 and 10 minutes after aroma inhalation than before inhalation. The amplitude ratio of F/M was significantly lower at 1 min after inhalation than before inhalation. All subjects liked the smell of lavender. Conclusion: In subjects inexperienced with aromatherapy, the excitatory state of spinal motor neurons innervating upper extremity was lowered after inhalation of lavender oil. To decrese muscle tone, therefore, physical therapy that suppress muscle tone may be more effective after inhalation of lavender oil.