We report a 56 year-old-woman with spinal cord infarction. She experienced left-sided girdle pain without precipitating symptoms and she developed monoparesis of her left leg and urinary retention. She also presented the segmental loss of total sensations in the Th10-11 area of the left trunk, the disturbance of position and vibration senses in the left leg and the disturbance of pain and temperature senses in the right leg. T2-weighted MR imagings showed high signal intensity lesion in the left half of the spinal posterior column at Th9-10 vertebral levels. Somatosensory evoked potentials confirmed that the loss of position and vibration senses was unilateral. Though she became able to walk with canes two months later, her sensory disturbance showed no improvement. This is a rare case of unilateral posterior spinal cord infarction presenting Brown-Séquard syndrome.