Progressive moyamoya disease in pregnancy and puerperium has not been reported previously. Here, we present a 39-year-old woman who had been found to have moderate stenosis of right middle cerebral artery (MCA) 4 years prior to her pregnancy, finally suffering minor completed stroke due to progressive moyamoya disease at the early postpartum period. Three days after cesarean section without any complication, she developed cerebral infraction at right hemisphere, when magnetic resonance angiography indicated apparent progression of the proximal MCA stenosis. Catheter angiography demonstrated nearly occlusion of the right terminal internal carotid artery (ICA) and the development of an abnormal vascular network at the base of the brain as well as MCA stenosis, indicating a definitive diagnosis of moyamoya disease with unilateral involvement. The patient underwent superficial temporal artery-middle cerebral artery anastomosis 1 month after the onset of stroke, and she did not manifest as further neurological events during the follow-up period of 2 years. Moyamoya disease could newly develop in pregnancy and puerperium, which should be noted as a pitfall of the management of moyamoya disease with pregnancy.