Respiratory drug particles aerosolized from Dry powder inhalers (DPIs) may charge electrostatically. Influence of electrostatic charge and aerodynamic size distributions on the regional deposition of inhaled aerosols in the lung has been acknowledged by the investigators of aerosol medicine research. This in vitro investigation reports a novel method of simultaneous measurement of both electrostatic charge and aerodynamic diameter of the particle in real time. The drug aerosols were generated by three commercially available and often prescribed DPIs by means of inhalation as a bolus at the rate of 30 L/min for 8 s, and then characterized by a Single Particle Aerodynamic Relaxation Time analyzer. The results showed that particles were not only varied sizes but also carried positive, negative and zero electrostatic charges. Aerosols generated by all three DPIs exhibited net electropositively charged.