Parkinson’s disease (PD) is associated with cardio- vascular autonomic dysfunction, but its effects on heart-rate variability (HRV) complexity remain incompletely understood. This study evaluated whether ECG-derived multiscale entropy (MSE) captures PD-related alterations in HRV complexity and transfers across cohorts. MSE was computed across 20 temporal scales from RR-interval-derived heart-rate series in a Chilean cohort of 72 participants (43 controls, 29 PD). PD participants showed lower short-scale MSE, mainly across scales 1–5. An MSE-only supervised pipeline was developed using Chile-only nested cross-validation and then applied unchanged to an inde- pendent Japanese wearable RR-interval cohort of 45 participants (21 controls, 24 PD), with no refitting, rescaling, feature selection, threshold optimization, or calibration using Japanese data. The Chilean pooled out-of-fold ROC AUC was 0.739 (95% CI 0.616– 0.857), and locked Japanese validation reached 0.810 (95% CI 0.667–0.933). At threshold 0.5, external sensitivity was 0.958 and specificity was 0.381. These findings suggest that short- scale HRV complexity carries PD-relevant autonomic information with partial cross-cohort transferability, supporting MSE as a complexity framework for wearable RR-interval studies.