A 69-year-old woman had syncope and aphasia. Magnetic resonance imaging showed multiple cerebral infarctions in both hemispheres. Cardiogenic embolisms were suspected, but no arrhythmic causes were shown. Transesophageal echocardiography revealed a highly calcified mitral annulus (MAC) with a rough intraluminal surface and mild mitral regurgitation, but no thrombus or tumor in the left heart system. However, recurrent multiple cerebral embolisms occurred in spite of strict anticoagulation therapy. We speculated that spontaneous rupture of the MAC was the cause of the scattered cerebral embolisms, and we therefore planned to remove the MAC as safely as possible and to endothelialize the deficit of MAC with autologous pericardium. Operative findings revealed that the MAC in P2-P3 had ruptured longitudinally and the ostium of the left atrium was connected to the ostium of the left ventricle as an inter-atrioventricular tunnel beneath the posterior mitral annulus with a fragile calcified wall. The finding suggested that calcified particles that had peeled away from the MAC by normal heart beating resulted in the cerebral infarctions. Therefore, she underwent resection of the MAC and mitral valve replacement with reinforcement of the decalcified posterior mitral annulus between the posterior left ventricular wall and the left atrial wall using autologous pericardium, which enabled both appropriate insertion of a mechanical prosthetic valve and endothelial continuity covering the surface of the residual MAC. No systemic embolism has occurred for two and a half years after surgery. This is the first case report of cerebral embolism caused by a spontaneously ruptured MAC.