Introduction: Thalassemia, a genetic hemoglobinopathy, results from a defect in globin chain production. It is characterized by ineffective erythropoiesis, and complications related to multiple transfusions can lead to higher morbidity. Accordingly, this study examines the correlation between pulmonary function and physical fitness in children with β-thalassemia major.Material and methods: This observational-correlation study was conducted between August 2022 to January 2023 at Abo EL-Reesh Al Mounira Hospital for children. The study included 34 children (17 boys and 17 girls) with β-thalassemia major, aged 6-10 years. The exclusion criteria included children with defined cardiovascular or respiratory disorders, renal failure, and recent thoraco-abdominal surgery or aneurysm. The following pulmonary functions were assessed using a spire spectrum neuro-soft spirometer: vital capacity (VC), maximal voluntary ventilation (MVV), forced expiratory volume in the first second (FEV1), and peak expiratory flow rate (PEF). Health-related physical fitness, as functional capacity, was measured by a 6-min walk test, with energy expenditure determined using the energy expenditure index (EEI). Skill-related fitness, as balance, was measured with a pediatric balance scale.Results: Pulmonary function was found to be significantly positively correlated with functional capacity and balance in children with β-thalassemia major (p < 0.05).Conclusions: Pulmonary rehabilitation is of significant value in children with β-thalassemia major.