Airway inflammation characterized as asthma is one of the most common chronic diseases in the world. The aim of this study was to evaluate the possible effect of inspiratory muscle training on inflammation markers and oxidative stress levels in childhood asthma. A total of 105 children (age range 8-17 years), including 70 asthmatics and 35 healthy children, participated in the study. The 70 asthma patients were randomly assigned to the inspiratory muscle training (IMT) group (n = 35) and control group (n = 35), and healthy children were assigned to the healthy group (n = 35). The IMT group was treated with the threshold IMT device for 7 days/6 weeks at 30% of maximum inspiratory pressure. Respiratory muscle strength was evaluated with a mouth pressure measuring device, and respiratory function was evaluated with a spirometer. In addition, CRP, periostin, TGF-β, and oxidative stress levels were analyzed. The evaluation was performed only once in the healthy group and twice (at the beginning and end of 6 weeks) in asthma patients. In the study, there were significant differences between asthma patients and the healthy group in terms of MIP and MEP values, respiratory function, oxidative stress level, periostin, and TGF-β. Post-treatment, differences were observed in the oxidative stress level, periostin, and TGF-β of the IMT group (p < .05)., Conclusion: After 6 weeks of training, IMT positively contributed to reducing the inflammation level and oxidative stress. This suggests that IMT should be used as an alternative therapy to reduce inflammation and oxidative stress. (Trial Registration: The clinical trial protocol number is NCT05296707)., What Is Known: • It is known that adjunctive therapies given in addition to pharmacological treatment contribute to improving symptom control and quality of life in individuals with asthma., What Is New: • There are no studies about the effect of respiratory physiotherapy on biomarkers in asthmatic children. The sub-mechanism of improvement in individuals has not been elucidated. • In this context, inspiratory muscle training has a positive effect on inflammation and oxidative stress levels in children with asthma and IMT should be used as an alternative treatment for childhood asthma., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)