[Purpose] The aim of the study was to determine the effect of xenon irradiation of the stellate ganglion region on fibromyalgia. [Subjects] The study included 5 men and 22 women (age, 56.4 ± 16.3 years [range, 25–84 years]) who were diagnosed with fibromyalgia according to the modified 2010 criteria of the American College of Rheumatology between July and August 2013. [Methods] Bilateral xenon light irradiation (0.38–1.1 μm) around the stellate ganglion was performed in the supine position by physical therapists using a xenon phototherapy device. We evaluated pain before and after irradiation using the visual analogue scale. [Results] We did not observe a relationship between the change in the visual analogue scale score and duration of fibromyalgia. However, we observed a relationship between the change in the visual analogue scale score and the score for the Japanese version of the Fibromyalgia Impact Questionnaire using the Cochran-Armitage test for trend. [Conclusion] Xenon light irradiation of the stellate ganglion significantly decreased the visual analogue scale score in patients with fibromyalgia having a higher score in the Fibromyalgia Impact Questionnaire, suggesting that a stronger effect could be obtained in patients with more severe fibromyalgia.