Purpose: The aim of our study was to investigate effects of end-expiratory positive pressure (PEEP) at varying degrees on respiratory mechanics, hemodynamic and intra-abdominal pressure in obese patients undergoing surgical intervention at prone position. Materials and methods: The study included 54 patients with BMI (Body Mass Index) ≥30 kg/m2who were scheduled for extra-abdominal surgery at prone position. The patients were randomly assigned into 3 groups as follows: PEEP was set to 0 cmH2 O in group 1; 5 cmH2 O in group 2; and 10 cmH2 O in group 3. The blood gas sampling was performed at supine position immediately before placing patient to prone position and in the prone position. Heart rate (HR), systolic arterial pressure (SAP), diastolic arterial pressure (DAP), mean arterial pressure (MAP) dynamical compliance, peak inspiratory pressure (PIP), plateu pressure (Pplateu), end tidal carbondioxide pressure (PETCO2), oxygen saturation (SpO2 ), tidal volume (VT) were recorded. Simultaneously, intra-abdominal pressure was measured. Measurements were repeated after patient placed into supine position from prone position. Results: When compared to supine period, compliance, SAP, DAP, MAP, HR and PETCO2 values measured at prone period were found to be significantly higher in all groups (p=0,02), (p=0,018), (p=0,013), (p=0,002), (p=0,02), (p=0,01), respectively) When compared to supine period, PIP and Pplateu values measured at prone period were found to be significantly higher (p=0,002) and (p=0,001), respectively). In binary comparisons, PIP and Pplateu values were found to be significantly higher in group 3 than group 1 (p=0,002) and (p=0,001, respectively). Conclusion: It was concluded that physiological PEEP administration will be beneficial in patients undergoing surgery at prone position; that it did not cause significant increase in intra-abdominal pressure and negatively affect hemodynamic, particularly in patients with high BMI; and that PEEP in physiological range improved oxygenation.