The aim of the work presented here was to determine the role of dry powder inhaler (DPI) counselling on inhalation technique and lung function test scores of the asthmatic patients. To decrease variability, asthmatic patients using an Aerolizer were enrolled in the study, as this was the most commonly prescribed DPI in outpatient clinics of Beni Suef University hospital. Each patient was subjected to three visits separated by 1 month each. In each visit, patient inhalation technique from the DPI was checked, and the number of mistakes was identified and corrected. Also, patients’ peak expiratory flow (PEF) and forced expiratory volume in one second (FEV1) presented as a percentage of the forced vital capacity (FVC) were checked. As the number of visits increased, the mean number of observed mistakes was significantly decreased (p < 0.001). The most common repeated mistakes were “To inhale fast” and “To maintain a fast inhalation rate until the lungs are full”. In all age groups, there was a significant increase (p < 0.001) in the pulmonary function test after the period of counselling. To improve and maintain the recommended inhalation technique of DPI and possibly improve patients’ lung function test scores, counselling on proper DPI technique should be repeated at every possible opportunity.