Parkinson's disease (PD) is a progressive multifactorial degenerative disorder that has both motor and nonmotor features. Among the nonmotor features of PD, cognitive impairment; Mild Cognitive Impairment (MCI) and dementia, poses one of the most significant implications for disability. Because of the high possibility of developing Dementia in PD, it is essential to obtain a reliable cognitive screen. Two commonly used cognitive measures include the Mini Mental Status Examination (MMSE) and the Montreal Cognitive Assessment (MoCA). The MoCA is a more sensitive tool for the detection of MCI in compared to the MMSE. Because of the cultural differences, in this study, we evaluated the psychometric properties of the Persian version of the MoCA (MoCA-P) in a group of participants with PD in Iran. Participants were assessed by MMSE, Geriatric Depression Scale (GDS), and Functional Assessment Staging Test (FAST). If they met study eligibility, the MoCA-P scale was administered. Receiver Operating Characteristic (ROC) curve analyses showed that the MoCA-P scale produced significant discrimination of PD with Dementia (PDD) from PD with MCI (PD-MCI). It seems that the MoCA-P has adequate psychometric properties as a screening instrument for the detection of PD-MCI and PDD in Iranian patients. As near to 30% of patients with PD go on to develop dementia, the MoCA-P can be useful in the detection of cognitive impairment in patients with PD and is suitable for executive function assessment.