Introduction: A number of indices have been proposed as accurate predictors of weaning, but several studies have questioned the accuracy of these weaning indices in predicting the capability of independent breathing. The purpose of the study was to assess six standard bedside weaning criteria of mechanically ventilated patients in Surgical intensive care unit (SICM). METHOD: : The study was performed on 72 SICU patients who were mechanically ventilated. According to the outcome of weaning, they were divided into two groups, weaning success (n=62) and weaning failure (n=10) group. All subjects should have PaO2 above 60 mm Hg at an FIO2 of 0.4 and PEEP of 3~5 cm H2O in the extubated patients and no PEEP in the tracheostomy patients. Six bedside weaning criteria were tidal volume above 5 ml/kg, respiratory rate below 25/min, vital capacity above 10 ml/kg, maximum inspiratory pressure below -20 cm H2O, minute volume below 10 L/min and PaO2/FIO2 above 200. Weaning failure was regarded as follows; changes of systolic blood pressure 20 mm Hg or diastolic pressure 10 mm Hg, changes of pulse rate 20 beat per minute, respiratory rate above 30 per minute or increased respiratory rate above 10 per minute, PaO2 below 60 mm Hg or PaCO2 above 55 mm Hg, and presence of paradoxical respiratory pattern. RESULTS: PaO2/FIO2 and minute volume (VE) were showed statistically significant difference between two groups (P=0.048, P=0.003 respectively). Linear discriminant function was D=-1.422-0.005-xPaO2/FIO2+0.336xVE. CONCLUSION: Our study demonstrates that PaO2/FIO2 and minute volume accurately predicts the weaning outcome in the surgical patients with mechanical support.