Differing from conventional approaches for improving sexual dysfunction of an adult man being commonly achieved by letting the adult man administer a dosage of synthetic drug or a composition of Chinese herbal medicines, the present invention particularly discloses a method for treating male sexual dysfunction by using underpants comprising far-infrared fibers. Clinical data have proved that, after wearing this underpants for 3 months, both the men diagnosed with sexual dysfunction and the men not sure to suffer from sexual dysfunction have an apparent progress on improvements of their erectile ability, erectile quality, ejaculation control ability, and lower urinary tract symptoms (LUTS). Moreover, clinical data have also proved that, despite the fact that a male person wears the underpants provided by the present invention for three months, there is no adverse effect induced by the underpants for causing the physiological condition of the men be abnormal.