The aim of the present study was to determine the efficacy, side-effects and tolerability of blonanserin for treating refractory behavioural psychological symptoms of dementia (BPSD). The present study was a 12-week, prospective, structured clinical trial of blonanserin for the treatment of BPSD. The degree of cognitive function, activities of daily living score, and the degree of BPSD were determined using the Mini-Mental State Examination (MMSE), Disability Assessment for Dementia (DAD), Neuropsychiatric Inventory (NPI) and the Rating Scale for Aggressive Behaviour in the Elderly (RAGE). The severity of extrapyramidal symptoms was assessed using the Drug-Induced Extrapyramidal Symptoms scale (DIEEPS). Five patients were enrolled. These patients met the NINCDS-ADRDA criteria. The patients were prescribed more than two kinds of existing antipsychotic drugs and were considered refractory cases; the drugs were discontinued because they were ineffectual and side-effects appeared. Each drug was prescribed independently for at least 2 weeks. The mean changes (at baseline and at the last week, respectively) in the MMSE (12.25, 9.25), in the DAD (6.5, 6.75), in the RAGE (5.5, 5.3) and in the DIEEPS (0.5, 1.5) were minimal. The mean changes in the NPI were two or fewer points. Some side-effects (one gait abnormality and one pneumonia) were observed. The results of this preliminary study show that blonanserin does not have adequate efficacy for the treatment of refractory BPSD.