Introduction: Pediatric patients, because of their anatomical differences in airway compared to adult pose many challenges during endotracheal intubation during general anesthesia. One such challenge is selecting the proper size of endotracheal tube for intubation. Objective: To assess the subglottic diameter by ultrasonography and compare with age based formula for selection of the appropriate size endotracheal tube in pediatric patients. Materials and Methods: 60 pediatric patients aged 5 to 15 years of both gender with normal airway, scheduled for surgery under general anesthesia and intubation, were included for this prospective clinical randomised study. Patients were divided randomly into Two groups of 30 each. In Group A (n = 30) estimation of endotracheal tube size was done by ultrasonography and patients were intubated by that size of tube. In Group B (n = 30) estimation of endotracheal tube size was done by age based Motoyama formula and patients were intubated by that size of tube. Time required for intubation, leak test for appropriate size endotracheal tube, hemodynamic parameters and peri-operative complications were studied. Results: In our study, in Group A 26 of 30 (86.66%) patients and in Group B 19 of 30 (63.33%) patients had appropriate size of tube as checked with the leak test, the P value (< 0.05) was significant. Conclusion: Ultrasound guided assessment of subglottic region is more reliable method to estimate appropriate size of endotracheal tube in pediatric patients.