Functional connectivity is a relatively novel technique of fMRI data analysis, which focuses on identifying connectivity between brain regions by analysing correlations of spontaneous fluctuations of brain activity across time. It was shown that brain regions that form functional networks show coherent BOLD fluctuations under resting conditions, and that this functional architecture is disturbed in various brain disorders. The aim of this study was to explore possible differences in brain connectivity in patients with mild cognitive impairment and Parkinson’s disease with and without PD related mild cognitive impairment, which could serve as diagnosis biomarkers in early stages of the disease. 72 participants—21 healthy individuals, 22 participants with mild cognitive impairment, 14 participants with Parkinson’s disease, 15 participants with Parkinson’s disease related mild cognitive impairment—underwent resting-state functional magnetic resonance imaging. Results of investigation of group differences in network connectivity and global brain integration will be reported and discussed.