A 51-year-old woman started taking Chinese medicine containing ephedara herba as a nasal decongestant. One week later, she had three episodes of thunderclap headache, one during defecation and the others while taking a bath. She then had a convulsive seizure upon resolution of the second headache. A cranial CT did not show subarachnoid hemorrhage. Repeated CSF examinations showed neither xanthochromia nor inflammation. Brain diffusion-weighted and FLAIR MR images revealed high intensity lesions in bilateral hemispheres. A cerebral angiography showed multifocal segmental stenosis of bilateral cerebral arteries. Four months later, follow-up angiography showed normalized flow in all cerebral arteries and we gave a diagnosis of reversible vasoconstriction syndrome (RCVS). She has had no symptoms and signs since the third attack of headache. RCVS is an important disease in the differential diagnosis of thunderclap headache without neurological deficit. This is the first report of RCVS triggered by Chinese herbal medicine.