Background: Inadequate ventilation, esophageal intubation and difficult intubation are the most common adverse respiratory outcomes in patient undergoing anesthesia .The aim of this study was to compare Mallampati test in supine and sitting positions in traditional approach and during phonation for predicting difficult laryngoscopy and intubation. Methods: In this study performed in Imam Khomeini Hospital in Tehran, Iran, Mallampati test was performed on 661 patients who met the inclusion criteria for the study. The test was done in supine and sitting positions with and without phonation by a rater who was blind to Mallampati test. Subsequently, laryngoscopy view and difficult intubation were evaluated in the four aforesaid positions by Mallampati test for predicting difficult laryngoscopy and intubation. For each situations, sensitivity, specificity, positive and negative predictive values and accuracy were calculated.Results: Overall, 28 (4.2%) patients had difficult laryngoscopy and 9 (1.4%) patients had difficult intubation. The highest sensitivity for Mallampati test in predicting difficult laryngoscopy and intubation was in supine and sitting positions without phonation, and the highest specificity was seen in sitting position with phonation. Negative predictive values were more than 95% in all different positions for Mallampati tests and the highest positive predictive value was seen in supine position with phonation.Conclusion: According to our findings, the highest correlation between Mallampati test and different positions in predicting difficult laryngoscopy and intubation was seen in supine position with phonation. Phonation improved Mallampati score in supine rather than sitting position.