BACKGROUND: Individuals with mild cognitive impairment (MCI) often exhibit progressive deficits in bimanual coordination and fine motor dexterity. However, the neural mechanisms underlying these motor impairments remain poorly understood. AIM: This cross-sectional study employed functional near-infrared spectroscopy (fNIRS) to examine cortical hemodynamic responses during fine motor tasks in MCI. METHODS: Thirty individuals with MCI and 40 age-, sex-, and education-matched healthy controls (HCs) performed the Nine-Hole Peg Test (NHPT) while fNIRS monitored oxygenated hemoglobin (HbO) and deoxygenated hemoglobin (HbR) responses in the prefrontal cortex (PFC), sensorimotor cortex (SMC), and visual cortex (VC). RESULTS: Compared to HCs, individuals with MCI exhibited significantly impaired NHPT performance, accompanied by reduced HbO responses in the right PFC and SMC during task performance. Furthermore, stepwise discriminant analysis identified a combination of right SMC HbO levels and NHPT scores as a significant predictor for distinguishing MCI from HCs, achieving an area under the curve (AUC) of 80.8%. CONCLUSIONS: These findings provide novel evidence linking aberrant cortical hypoactivation in the motor and executive control regions to fine motor impairments in individuals with MCI, suggesting disrupted motor-cognitive integration in early cognitive decline. The integration of fNIRS-derived hemodynamic responses with functional motor assessments offers a promising non-invasive approach for MCI detection and personalized rehabilitation. TRIAL REGISTRATION: This study was registered with the Chinese Clinical Trial Registry (Registration No. ChiCTR2400082429) on March 28, 2024.