Purpose To evaluate cardiorespiratory fitness in patients with early to mid-stage Parkinson’s disease by cardiopulmonary exercise test (CPET) on a stationary cycle ergometer. Methods To compare the differences in each index of the cardiopulmonary exercise test between the two groups of subjects; general data such as disease duration, medication use and exercise habits were also collected. Results (1) Finally, 36 Parkinson’s disease patients and 12 healthy controls successfully completed the cardiopulmonary exercise test without any adverse events. (2) The V’O2peak, Metspeak, RERpeak, MVVpeak, Wpeak, HRpeak, HRpeak/pre, percentage of HRR-1 min decay > 12 bpm, SBPpeak in the Parkinson’s disease group were lower than those in the control group (p < .05, each). Detailed data: V’O2peak (15.7 ± 4.5vs21.5 ± 3.6 ml/kg/min, p < .01), Metspeak (4.5 ± 1.3 vs 6.1 ± 1.0, p < .01), RERpeak (1.04 ± 0.10 vs 1.15 ± 0.10, p = .001), MVVpeak (37.22 ± 11.58 vs 53.00 ± 16.85L/min, p = .009), Wpeak (49.17 ± 29.72 vs 49.17 ± 29.72W, p < .01), HRpeak (111.08 ± 16.67 vs 111.08 ± 16.67bpm, p < .01), HRpeak/pre (71.19 ± 10.06 vs 96.00 ± 21.13, p = .002), percentage of HRR-1min decay > 12bpm (33.3% vs 100%, p < .01), systolic blood pressure (155.81 ± 31.83 vs 175.83 ± 17.84 mmHg, p = .01). (3) Divided Parkinson’s disease patients into high V’O2peak group (V’O2peak ≥ 15 mL/kg/min) and low V’O2peak group (V’O2peak < 15 mL/kg/min). The age of patients, Hoehn–Yahr grade and incidence of symptom fluctuation in high V’O2peak group were lower (p < .05, respectively), percentage of males and percentage of HRR-1 min decay > 12 bpm were higher (p < .05, respectively); p < .05 is considered a statistically significant difference. Detailed data: age of patients(61.05 ± 6.93 vs 68.57 ± 7.99 years, p = .005), Hoehn–Yahr grade(1.75 ± 0.48 vs 2.18 ± 0.64, p = .028), incidence of symptom fluctuation (59.1 vs 92.9%, p = .03), percentage of males (77.7 vs 42.9%, p = .041), percentage of HRR-1 min decay > 12 bpm (50 vs 7.1%, p = .008). Conclusions Cardiopulmonary exercise test was safe to perform and the cardiorespiratory fitness is significantly reduced in patients with early and middle stage Parkinson’s disease. Patients with Parkinson’s disease presented blunted heart rate and systolic blood pressure responses to exercise test. Females, older age, fluctuating symptoms, high H-Y staging and higher activities of daily living may be associated with lower oxygen uptake.