The aim of this study was to find out the utility of Bedside Lung Ultrasound (BLUE) PROTOCOL in diagnosing the pathology of acute respiratory failure in patients presented to the emergency department. This is observational study was conducted in emergency department. We performed BLUE PROTOCOL on patients admitted in Emergency department with acute respiratory failure. All the patients above the age of 12 years were included. Results obtained by the BLUE PROTOCOL and final diagnosis done by the clinical experts were compaired. Rare ,uncertain diagnosis or multiple diagnosis were excluded. diffuse B lines with lung sliding indicating pulmonary edema can be diagnosed with sensitivity of 93% and specificity of 97%. Normal profile plus deep venous thrombosis indicates pulmonary embolism with sensitivity of 80% and specificity of 97%. Pneumothorax shows absent lung sliding plus A lines plus lung point can be diagnosed with sensitivity of 66% and specificity of 100%. B’ profile, A/B profile, C profile, A profile plus PLAPS indicates pneumonia whose sensitivity in diagnosis is 95% and specificity 97%. COPD and Asthma seen as A line plus lung sliding have sensitivity of 90% and specificity 100%. BLUE PROTOCOL had diagnostic accuracy of 90.5% in patients of acute respiratory failure. Faster results is the essence of BLUE PROTOCOL.