Abstract: Objective: Memantine has been reported to have positive effects on visual hallucinations and cognition in patients with dementia with Lewy bodies (DLB). We hypothesized that memantine would have similar effects on a patient having Charles Bonnet syndrome, preclinical DLB.Method: We evaluated the effect of memantine on visual hallucination, cognitive abilities and so on from baseline to 4 months after the start of medication.Results: Treatment of the patient with memantine resulted in the disappearance of visual hallucinations but could not stop the progression to dementia.Conclusions: Our results suggested that, for a patient having preclinical DLB, memantine had some degree of positive effects, but the mechanism remains to be revealed.