Background and Purpose: REM sleep behavior disorder (RBD) in Parkinson’s disease (PD) is associated with characteristic clinical subtypes and prognosis. In addition, nigrostriatal pathway, the most vulnerable anatomical area in PD, formed neuronal network interplaying with cortical and subcortical structures, and which may cause PD clinical phenotype. We evaluated the regional selectivity of presynaptic striatal dopaminergic denervation associated with RBD in PD. Methods: We compared two groups (n = 16) of PD patients with and without RBD in terms of specific binding ratios (SBR) in subregions of the striatum, which were measured using positron emission tomography with 18F-FP-CIT. SBRs of the anterior and posterior caudate, ventral striatum, and posterior and ventral putamen regions were measured in more or less affected side, and right or left side, or bilateral sum of the striatum. Results: Age, disease duration, and severity of parkinsonism were not significantly different between groups. Although group differences in all areas were not significant with multiple comparison corrections, SBR of the ventral striatum and anterior caudate in sum of both sides was significantly less in the RBD than in the non-RBD group without correction (p 0.05). In the right anterior caudate and left ventral striatum, SBR was also lower in the RBD than in the non-RBD group without correction (p 0.05). Attention function was impaired in the RBD group compared with the non-RBD group (p 0.05). However, these statistical significances were not definite after correction of multiple comparisons (p \mathrm{>} 0.05). Conclusions: There is a possibility that RBD in early PD may be associated with presynaptic dopaminergic denervation in the ventral striatum and anterior caudate, which may explain decreased attention in our RBD group. RBD in PD may imply a distinct pathological progression. However, further study using large numbers of participants or longitudinal observation is necessary for the statistical conclusion because of small sample size.