Background: The purpose of this study was to evaluate the effect of threshold INSPIRATORY MUSCLE TRAINING , ((IMT)) on the duration of weaning in intensive care unit ,(ICU)‑, admitted patients. Materials and Methods: This randomized clinical trial enrolled 79 ICU‑, admitted, mechanically ventilated patients in 2020–, 2021 in Imam Reza Hospital, Mashhad. Patients were randomly divided into intervention , (n , = , 40) and control , (n , = , 39) groups. The intervention group received threshold (IMT) and conventional chest physiotherapy, while the control group only received conventional chest physiotherapy once a day. Before and after the end of the intervention, the strength of INSPIRATORY MUSCLEs and the duration of weaning were measured in both the groups. Results: The duration of weaning was shorter in the intervention group , (8. 4 , ±, , 1. 1 , days) versus the control group , (11. 2 , ±, , 0. 6 , days) , (P , < , 0. 001). The rapid shallow breathing index decreased by 46. 5% in the intervention group and by 27. 3% in the control group after the intervention , (both P , < , 0. 001), and the between‑, group comparison showed a significantly higher reduction in the intervention group than control group , (P , < , 0. 001). The patients’,compliance after the intervention compared to the 1 st , day increased to 16. 2 , ±, , 6. 6 in the intervention group and 9. 6 , ±, , 6. 8 in the control group , (both P , < , 0. 001), and the between‑, group comparison showed a significantly higher increase in the intervention group than control group. The maximum INSPIRATORY pressure increased by 13. 7 , ±, , 6. 1 in the intervention group and by 9. 1 , ±, , 6. 0 in the control group , (P , < , 0. 001). Furthermore, the weaning success was 54% more probable in the intervention group than control group , (P , < , 0. 05). Conclusion: The results of this study showed the positive effect of (IMT) with threshold (IMT) trainer on increased strength of respiratory MUSCLEs and reduced weaning duration.