Objective: Vasospasm remains the leading cause of cerebral damage after aneurysmal subarachnoid hemorrhage. Although magnesium regulates the calcium influx in vascular smooth muscle and endothelial cells, it has not been reported whether L-type calcium channels are involved in magnesiuminduced vascular relaxation in rat basilar artery. So, the effect of magnesium sulfate on L-type calcium currents in freshly isolated smooth muscle cells from rat basilar artery was investigated. Methods: The smooth muscle cells were isolated from rabbit basilar artery by enzyme treatment. L-type Ca2+ currents were identified using cesium chloride, a potassium channel blocker and Bay K8644, an activator of L-type Ca2+ channel. Currents were recorded under step pulse whole cell patch clamp technique. Results: In the presence of cesium chloride (in pipette solution), inward currents were observed by depolarizing step pulses. The inward currents were significantly reduced by nimodipine (n=4, p<0.05), an L-type Ca2+ channel blocker and increased by Bay K8644 (n=5, p<0.05), an L-type Ca2+ channel activator. The L-type calcium currents (156±17.0 pA, n=12) were significantly reduced by the application of 5 mM magnesium sulfate (53.8±7.0 pA, n=12, p<0.01). Conclusion: These results suggest that magnesium may relax cerebral vessel of rat basilar artery through decreasing intracellular Ca2+ ion by inhibition of L-type Ca2+ channels.