Background: Recently, heated humidified high flow nasal cannula (HFNC) has gained popularity, and is now considered as standard respiratory support for pediatric patients with acute respiratory distress. However, there is limited data concerning bedside parameters for prediction of HFNC failure in pediatric patients. Material and method: A prospective observational study was conducted in 1 month to 15 year old patients with acute respiratory distress that required high flow nasal cannula support. The setting of high flow nasal cannula, vital signs, clinical respiratory score and the outcome of treatment were recorded. Data were analyzed to determine the predictors of HFNC failure. Results: In total 82 children participated in the study; from which 16 children (19.5%) did not response to high flow treatment (failure group). Pneumonia was the main reason for intubation (62.5%). Predictors of high flow nasal cannula failure at 12 hours were: SF index ≤ 166 (sensitivity 87.8%, specificity 62.5%, AUC 0.75), pROX index < 132 (sensitivity 84.8%, specificity 68.7%, AUC 0.77), and clinical respiratory score ≥ 6 (sensitivity 87.5%, specificity 96.9%, AUC 0.92). Conclusion: The clinical respiratory score is the most accurate predictor of high flow nasal cannula failure in pediatric patients. A clinical respiratory score of more than 6, at 12 hours, is a helpful indicator for high flow nasal cannula failure. pROX index, and the newly modified parameters in this study are also good for prediction of high flow nasal cannula failure Keyword: High flow nasal cannula, predictors, acute respiratory distress children