Asthma is a chronic condition characterized by inflammation throughout the entire bronchial airways. Recent findings suggest that ventilation inhomogeneity and small airway dysfunction (SAD) play a particularly significant role in asthma development and clinical manifestations. Obesity is a considerable risk factor for asthma development and morbidity in children and adults. A growing body of evidence suggests that SAD is linked to more severe asthma and poor asthma control in obese patients. However, the knowledge about the relationship between peripheral airway compromise and obesity in asthma is limited, mainly because of the historical lack of access to non-invasive assessment methods for studying SAD. Conventional lung function measurements, like spirometry, cannot accurately assess small airway function. However, in recent years, new specialized tests available in outpatient settings have been found to distinguish SAD from large airway obstruction more accurately compared to spirometry. Therefore, understanding the degree of peripheral airway implication in the underlying pathology is critical for effective asthma control and therapeutic decisions. This review highlights recent findings on the impact of SAD on asthma patients who are obese. Additionally, it explores how new diagnostic methods, such as impulse oscillometry (IOS), may be used in outpatient settings to detect small airway impairment in obese asthma at an early stage, potentially leading to improved asthma treatment.