Pharmacotherapies for the behavioural and psychological symptoms of dementia are limited; novel agents for the symptoms are still needed. Herein, we report the case of an 80-year-old male patient with Alzheimer's disease whose severe agitation, insomnia and sexual delusions were successfully treated with a traditional natural Japanese (Kampo) medicine, keishi-ka-ryukotsu-borei-to. We found that administrating keishi-ka-ryukotsu-borei-to increased his serum luteinizing hormone level, which could be inversely associated with his behavioural and psychological symptoms. This report suggests that keishi-ka-ryukotsu-borei-to is a possible alternative treatment for the behavioural and psychological symptoms of dementia, especially sexual delusions.