Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by significant cognitive and behavioral impairments. Near-infrared (NIR) light treatment has shown potential in cognitive improvement in previous studies. However, clinical trials of NIR for AD remain limited.This study investigated the safety and effects of whole-head 810 nm NIR therapy in AD patients, including long-term efficacy.An open-label pilot study on whole-head NIR treatment for AD patients was conducted. Nine AD patients completed 4-month treatment (810 nm, 100 mW/cm², 30 min/session, 6 sessions weekly). Safety and efficacy were evaluated at baseline, months 2 and 4, and 2-month post-treatment.After four months of whole-head NIR treatment, mean changes from baseline on the Mini-Mental State Examination were 3.2 (p = 0.02). Mean changes from baseline on the Alzheimer's Disease Assessment Scale-Cognitive were -5.0 (p = 0.05), mean changes from baseline on the Montreal Cognitive Assessment were 1.9 (p = 0.12). Mean changes from baseline on the Neuropsychiatric Inventory were -4.2 (p = 0.47). These benefits were sustained two months at least. With no device-related adverse effects were reported.Whole-head 810 nm NIR light is safe and offers promising benefits for AD patients. To fully confirm its efficacy, durability, and underlying mechanisms, further large-scale randomized controlled trials are necessary.