We report a case of obstructive sleep apnea improved with the treatment both of Kampo medicine and Western medicine. The patient aged 52 years old was struggling with daytime drowsiness. Through the sleep test, he was diagnosed as severe obstructive sleep apnea (OSA) and was received a continuous positive airway pressure therapy (CPAP). Generally, positive air from CPAP applies through the nose and usage reports were recorded in the device. If having nasal congestion, it may be hard to continue CPAP. In this case he had a severe nasal congestion, and he nearly became CPAP failure. It was clear from the poor usage reports. Using Eppikajutsuto for nasal congestion, he felt decrease of nasal congestion. By switching to Shoseiryuto or kakkontokasenkyusin’i from Eppikajutsuto with reference to CPAP usage and nasal CT images, CPAP was continued effectively. Eventually, his daytime sleepiness disappeared.To continue CPAP, which is one of Western medicine, Kampo medicine was useful. On the other hand, to evaluate the effectiveness of Kampo medicine, Western medicine was necessary. CPAP reports and nasal CT images, which are Western medicine, contributed to the switch to Kampo medicine. This case showed the worth of the combined therapy of Kampo medicine with Western medicine.