AbstractParkinson's disease (PD) patients frequently suffer from insomnia and insomnia can result in reduction of quality of life in PD. Although pharmacotherapy is most applicable for insomnia, it may cause side‐effects in PD. The purpose of the study was to investigate the efficacy of brief cognitive behavioral therapy for insomnia (CBTI) in PD. A total of 11 PD patients aged 43–84 years with chronic insomnia received two sessions of CBTI. Patients reported a significant decrease in total score for the Insomnia Severity Index (ISI). The total score for the Parkinson's Disease Sleep Scale (PDSS) improved. Although objective sleep measured by actigraph did not improve, subjective sleep measured by sleep diary improved. Functional impairment measured by the Sheehan Disability Scale (SDS) significantly decreased. These results revealed that brief CBTI was effective in improving insomnia in PD, with improvements extending to functional impairments that had been affected by insomnia. Additionally, this non‐pharmacotherapy treatment could be easily applied to PD patients who may have difficulty coming to the clinic frequently due to physical symptoms.