BACKGROUND: Apathy impacts mood and social functioning in patients with Parkinson's disease (PWP), and its effect on motor rehabilitation outcomes remains unexplored. OBJECTIVE: This study evaluates whether the presence of apathy (apathy status) is associated with rehabilitation outcomes in PWP. METHODS: We retrospectively analyzed records of 122 PWP (Hoehn-Yahr stage ≤ 3) who underwent a 2-week multidisciplinary intensive rehabilitation treatment (MIRT) between April 2020 and July 2024, dividing them into Parkinson's disease with apathy (PDA+, score > 14) and without apathy (PDA-, score ≤ 14) based on Modified Apathy Evaluation Scale (MAES). The outcome measures included the Movement Disorder Society Unified Parkinson's Disease Rating Scale part III (MDS-UPDRS III), the Modified Parkinson Activity Scale (M-PAS), the Five Times Sit to Stand Test (FTSTS), the Timed Up and Go Test (TUG), and the 10-Meter Walk Test (10MWT). We conducted group comparisons and employed multiple linear regression analyses, treating the MAES both as a dichotomous variable and as a continuous predictor. In these analyses, we adjusted for baseline measures of MDS-UPDRS III, FTSTS, and TUG. Additionally, we performed sensitivity analyses using alternative cutoffs (MAES > 13 and > 15). RESULTS: Following MIRT, the PDA- group (n = 75) showed significant improvements in MDS-UPDRS III, M-PAS, FTSTS, and TUG (p < 0.001, p < 0.001, p = 0.011, and p < 0.001, respectively). In contrast, no such improvements were observed in the PDA+ group (n = 47). The improvements in MDS-UPDRS III, FTSTS, and TUG scores exhibited significant differences between the groups (p = 0.018, p = 0.046, and p = 0.042, respectively). In multivariable linear regression with MAES as a continuous variable, higher MAES was independently associated with smaller ΔMDS-UPDRS III (β = 0.147, 95% CI 0.017-0.277, p = 0.027; R2 = 0.145), after adjustment for baseline MDS-UPDRS III, FTSTS, and TUG. Modeling MAES dichotomously (> 14 vs. ≤ 14) produced similar results (β = 2.378, 95% CI 0.341-4.415, p = 0.023; R2 = 0.148). Sensitivity analyses using cutoffs of > 13 and > 15 yielded qualitatively comparable findings. CONCLUSIONS: Baseline apathy severity was associated with attenuated motor improvement after MIRT in PWP; understanding its mechanisms is crucial for personalized rehabilitation and treatment effectiveness. TRIAL REGISTRATION: ClinicalTrials.gov identifier: ChiCTR2000033768, 2020/06/11.