Aneurysms of the superficial temporal artery are rare, and usually traumatic in origin. We present a very rare case of spontaneous dissecting aneurysm of the superficial temporal artery in a 46-year-old man. The patient had pulsatile headache in the right temporal region, and a pulsatile mass in the same region. His headache gradually worsened for which he came to our hospital. On examination, there was a pulsatile mass of 1.5cm x 3cm at the right temporal region, which disappeared when the main trunk of superficial temporal artery was compressed. There was no neurological abnormality. On computed tomographic examination, there was a spotty high density area in the right extracranial region corresponding to the right superficial temporal artery, which was strongly enhanced after contrast medium administration. On MRI examination, the same area showed high intensity, but at inner space there was signal loss on T1WI, T2WI and PDWI. Angiography showed an aneurysmal dilatation at the right superficial temporal artery and both the true lumen and the false lumen were recognized. Excision of the aneurysm under local anesthesia was performed. His complaints disappeared completely post-operatively, and the skin color of that region retained its normal texture. Histopathological examination of the specimen showed hypertrophic intima with fibroblasts, and absence of internal elastic lamina. There was hematoma outside of the intima, but no deposits of hemosiderin. On account of the above findings, the lesion was diagnosed as a spontaneous dissecting aneurysm of the superficial temporal artery.