Acute respiratory failure due to pneumonia is a significant cause of death in children 6-18 years old.; Objective - to find out whether diaphragm dysfunction might lead to unsuccessful weaning from MV in children 6-18 years old.; We provided prospective observational cohort study and included 104 patients, who were splitting in the study and the control groups and 2 age subgroups. To consider diaphragm function, we check amplitude of its movement and diaphragm thickening fraction (Dtf).; The primary outcome was the incidence of successful weaning from MV. The secondary outcomes were changes in diaphragm function parameters.; Dtf for right hemidiaphragm was significantly lower in the study group 1st subgroup on day 1 and day 5, and significantly higher on day 14 (p<0.05), while for left hemidiaphragm it was significantly higher on day 1 and lower on day 5 compared with the control group (p<0.05). In 2nd subgroup Dtf was significantly higher for both sides in the study group on day 1 compared with the control group (p<0.05). ; Amplitude of diaphragm movement was significantly decreased in 1st subgroup of the study group on day 1 and day 5 and increased on day 14 compared with the control group (p<0.05).; The incidence of successful weaning from MV in the study group was significantly lower compared with the control group.; Diaphragm dysfunction might alter weaning from MV in children 6-18 years old.