Background: Lung ultrasound is an increasingly used tool for monitoring pulmonary lesions or improving the diagnosis of pneumonia in critically ill children. This study aimed to assess the prognostic value of lung ultrasound scoring system in critically ill children. Methods: This prospective cohort study included 52 children on mechanical ventilation that were admitted at pediatric intensive care unit (PICU), Zagazig University Hospital. The Pediatric Risk of Mortality scores (PRISM III) were calculated within 24 hours of PICU admission. Pulmonary Ultrasound examinations was performed at 3 time points during a patient's ICU stay; as soon as possible after intubation, 48 hours after the initial examination and at extubation. Results: Duration of intubation ranged from 3 to 11 days with median (IQR) of 5 (2.25), while duration of ICU stay it ranged from 3 to 13 day with median (IQR) of 6 (4) and duration of hospital stay ranged from 4 to 33 days with median (IQR) of 10(10.25). As regard outcome; (59.6%) of the patients died, while (40.4%) of the patients were discharged from ICU. There was highly statistically significant positive correlation between first total US score and duration of ICU stay and ventilation days (p-value<0.001). Also, ROC curve analysis used to differentiate discharged from died patients by using second US score, at cut point 12, it showed sensitivity of (93.55%), specificity of (76.19%) with AUC of (0.940). Conclusion: Pulmonary Ultrasound scoring system is good prognostic tool in children with acute respiratory failure and predicting mortality and assessment of treatment response.