This study aimed to investigate the association between respiratory mechanics and autonomic modulation in morbidly obese patients. We evaluated 10 morbidly obese subjects (BMI=52.9+/-11.2kg/m(2)), aged 23-58 years. Assessment of respiratory mechanics was done by the forced oscillation technique (FOT), and cardiovascular autonomic function was recorded by heart rate variability analysis (HRV). The Pearson correlation coefficient was used to test the associations between respiratory mechanics and HRV variables. There were associations between the standard deviation of all RR intervals (SDNN) and airway resistance (Rm) (r=-0.82; p=0.004), SDNN and respiratory system resistance (R0) (r=-0.79; p=0.006), root mean square of successive differences between adjacent normal RR intervals (rMSSD) and respiratory system resistance (R5) (r=-0.643; p=0.0451), rMSSD and R0 (r=-0.64; p=0.047), and rMSSD and Rm (r=-0.658; p=0.039). We concluded that the airway and respiratory system resistances are negatively associated with parasympathetic activity in patients with morbid obesity.