Introduction: The application of NIV in the management of patients with acute respiratory failure is not associated with a 100% success rate. In many patients, application of NIV is clearly insufficient as it does not obtain adequate ventilation and eventually endotracheal intubation and invasive mechanical ventilation is required for the management of respiratory failure. Failure to identify the patients who are likely to fail NIV can cause inappropriate delay in intubation; this can lead to clinical deterioration and increased morbidity and mortality. The failure rates of NIV can range from 5% to 50% in different studies depending on the etiology and severity of respiratory failure. Objective: To evaluate initial Arterial blood gas as a predictor of successful NIV outcome in patients with type 2 respiratory failure in a tertiary care hospital in south Kerala. Methods: Based on longitudinal observational study, 80 adult patients diagnosed with Type 2 Respiratory failure were admitted to hospital requiring NIV. NIV-PSV (pressure support mode) were used in all patients. All patients were given oxygen and titrated during ventilation to maintain oxygen saturation between 88%-92%. Serial ABG were studied and if clinical or ABG value worsening were noted, they were proceeded for invasive ventilation. Weaning was initiated on clinical improvement and corroborative ABG values. Results: Out of the 80 patients admitted with type 2 respiratory failure, success rate with NIV was found to be 77.5% with 62 patients discharged successfully. Failure rate was 22.5% (18 patients). Of the failed 18 patients, 17 were mechanically ventilated and 1 expired on NIV as no consent for endotracheal intubation were given by the bystanders. 6 other patients who were mechanically ventilated also eventually succumbed. Patient with initial pH between 7.30-7.35 had shown better outcome (71%) as compared to pH between 7.25-7.30 which was statistically significant, p<0.001(Chi Square test) and with initial PaCo2 between 45-85 mmHg had shown better outcome (67.7%+29%) as compared to patient with initial PaCo2>85 and it is statistically significant, p<0.001(Chi Square test). Conclusion: Present study suggests that NIV is highly effective in treating patients with type 2 respiratory failure with pH 7.25-7.35. This study also shows that patients with high initial PaCo2 and low pH have lower chance of success with NIV. Study indicates that a trial of NIV is effective in improving gas exchange, reducing intubation in patients with type 2 respiratory failure, suggesting that NIV is a safe and effective means of ventilator support for patients with type 2 respiratory failure. The study provides strong evidence for the use of NIV as a first line intervention in patients with type 2 respiratory failure, irrespective of the cause of respiratory failure.