To elucidate the role of basal forebrain (BF) in non-motor symptoms of Parkinson's disease (PD), we investigated the association of sleep quality and cognition with BF volume and functional connectivity. The gray matter volume of the anterior intermediate part (Ch4ai) and the anterior lateral part (Ch4al) of the nucleus basalis Meynert were negatively associated with the PSQI global score. The posterior part of the nucleus basalis Meynert (Ch4p) volume was positively associated with visuospatial, memory, and executive functions. The PSQI global score correlated positively with functional connectivity from the Ch4al to the posterior cingulate, inferior parietal, anterior temporal, and medial prefrontal cortices, which correspond to the default mode network. Our results demonstrated that reduced volume of the anterior portion of the Ch4 and its aberrantly increased functional connectivity with the default mode network were closely related to poor overall sleep quality, while reduced volume of the posterior portion of the Ch4 was associated with decreased cognitive function in PD.