Abstract Mild cognitive impairment (MCI) is common in patients with Parkinson’s disease (PD), yet the underlyingneural mechanisms of this disease state remain unclear. Weinvestigated alterations in the spontaneous brain activity ofPD patients with MCI (PD-MCI) relative to cognitivelynormal PD patients (PD-CN) and healthy control (HC)subjects. In this work, 13 PD-MCI patients, 16 PD-CNpatients, and 16 HC subjects completed resting statefunctional MRI. Spontaneous brain activity was measuredby calculating amplitude of low frequency fluctuation(ALFF) values across the whole brain. Between-groupdifferences and correlations between ALFF values andcognitive test scores were analyzed. ALFF valuesdecreased in the right superior temporal gyrus andincreased in the left middle temporal gyrus anperior frontal gyrus of PD-MCI patients compared withPD-CN patients. In the PD-MCI group, ALFF values in theleft middle temporal gyrus were negatively correlated withMontreal Cognitive Assessment and vocabulary test scores,and the ALFF values in the left perior frontal gyrus of PD-MCI patients compared withPD-CN patients. In the PD-MCI group, ALFF values in theleft middle temporal gyrus were negatively correlated withMontreal Cognitive Assessment and vocabulary test scores,and the ALFF values in the left superior frontal gyrus werenegatively correlated with vocabulary test scores. Ourstudy demonstrates that PD-MCI is associated withabnormal spontaneous brain activity in the temporal and frontal lobes. These findings inform the underlying neuralmechanism of cognitive impairment in PD