Objective: To evaluate respiratory functions in children with cat sensitization using impulse oscillometry (IOS) and spirometry and to compare these with those of healthy controls. Methods: This prospective case-control study included 130 children aged 3-17 years with cat sensitization (CS group) accompanying respiratory allergic diseases (Group I: asthma, Group II: allergic rhinitis, and Group III: co-existent asthma and allergic rhinitis), and 70 age- and sex-matched healthy controls (HC group). The cases’ demographic parameters were recorded, and respiratory functions were analyzed using IOS and spirometry. The association between IOS and spirometric parameters was also evaluated. Results: At IOS evaluation, zR5, R5-20, Fres, and AX values were higher in children in the CS group compared to the HC group (p=0.029, p=0.008, p=0.001, and p<0.001, respectively), while zX5 and zX20 values were lower (p=0.001 and p<0.001). R5-20 and AX were higher in asthma compared to allergic rhinitis (p=0.008, 0=0.015), but were insignificant compared to both together. R5-20, Fres, and AX were higher, and zX20 was lower in the pre-school age group (p<0.001). No correlation was found between zFEV1, zFVC, zFEV1/FVC, zFEF25-75 and zR5 values in the CS group (p>0.05). Conclusions: Pulmonary resistance was higher and reactance was lower in the entire and peripheral airways in children with cat sensitization accompanying respiratory allergic diseases compared to the healthy controls. Peripheral airway resistance and reactance were more impared in asthma group compared to allergic rhinitis. However, peripheral airway resistance and main airway reactance were more impaired in the pre-school age group than in the older age group.