Herein, we describe a technique for stent-assisted coil embolization with a spring-shaped microcatheter in a patient with an M1 ultrawide-necked circumferential aneurysm in the middle cerebral artery (MCA). A 49-year-old man was referred for treatment of an incidentally detected M1 large-circumference aneurysm on magnetic resonance angiography. Subsequent digital subtraction angiography revealed an 18.2×16.5 mm ultrawide-necked circumferential aneurysm on the distal M1 portion of the left MCA, and we planned stent-assisted coil embolization using a spring-shaped microcatheter. After we deployed the stent, we performed coil embolization under the down-the-barrel view by pulling out the microcatheter little by little. Using this technique, we could fill the coil mass evenly into the aneurysmal sac around the stent. And there were no immediate or delayed complications after the procedure. Stent-assisted coiling using a spring-shaped microcatheter is a useful and safe technique for treating ultrawide-necked circumferential aneurysm or fusiform aneurysms.