Recent quantitative EEG (qEEG) analyses in Parkinson’s disease (PD) are reviewed. We reported the first qEEG evaluation in PD not only employing multiple logistic regression analysis but also estimating the distribution of qEEG changes in 2008. We evaluated the spectral ratio, i.e. the total of the absolute power values in the α and β waves divided by the total of the δ and θ waves values. The spectral ratios at all electrode locations excluded the frontal pole were presented to be the significant predictive variables in PD. PD presented diffuse slowing in the qEEG as compared to age-adjusted normal controls. We also evaluated the relation between the progression of PD and qEEG in 2009. The spectral ratio was significantly decreased according to the progression of PD at all the electrode locations. Moreover, we studied qEEG alterations in PD patients with executive dysfunction (ExD) in 2010 and cognitive impairment in 2011. An increase in slow wave was exhibited in frontal and frontal-pole locations in ExD and presented in all locations in dementia. It has been recently reported that qEEG finding has potential as a predictive biomarker for dementia incidence in PD in 2011.The qEEG analysis was thus not only a useful tool to study pathophysiological findings, but also a predictive biomarker for dementia.