There are very limited methods of relieving dyspnea that are independent of the causative disease. L-menthol olfactory stimulation is reported to be effective for dyspnea during exercise and inspiratory resistance. Therefore, we examined the effects of L-menthol olfactory stimulation on exertional dyspnea during the 6 min walking distance test (6MWT) in patients with chronic breathlessness syndrome. The subjects who consented to the study were divided into two groups. In Group A, the first 6MWT was performed as usual (placebo) while wearing a surgical mask, and the second 6MWT was performed under the L-menthol condition. In Group B, the first 6MWT was performed under the L-menthol condition, and the second 6MWT was performed as a placebo. A total of 16 subjects (70.8 ± 9.5 years) were included in the analysis. As for the effect of reducing dyspnea, a significant difference was observed in Group A patients who underwent the L-menthol condition in the second 6MWT (p = 0.034). In the comparison of the 6 min walking test under the L-menthol condition and the placebo, the modified Borg scale gain was significantly different between the L-menthol condition and the placebo (p = 0.007). Our results suggested that the L-menthol olfactory stimulation reduced dyspnea on exertion in patients with chronic breathlessness syndrome.