Background: particle formation mechanisms and aerosol performance of solution-based pressurized metered dose inhalers (pMDIs) are dramatically changed when ethanol is introduced in the formulation. The current study is to investigate the effect of ethanol on particle formation and aerosol performance of solution pMDIs using different pharmaceutical compounds. Methods: the aerosol performance of solution pMDIs containing beclomethasone dipropionate, fluticasone propionate and caffeine, with different ethanol concentrations and doses was evaluated using aerosol cascade impaction. The surface and internal structures of the particles were examined using Scanning Electron Microscopy (SEM) and Focus Ion Beam – Scanning Electron Microscopy (FIB-SEM). Results: the aerodynamic performance of the experimental formulations showed a significant reduction as the ethanol concentration in a formulation was increased. Particles produced from two corticosteroid formulations were amorphous with two different types of morphology – smooth surface with a solid core and coral-like with porous internal structure. Caffeine particles were crystalline with elongated morphological feature. Conclusion: due to the difference in ethanol concentration in emitted droplets, residual particles from solution pMDIs may have distinct drying process: droplets with less ethanol will be dried during the propellant/ethanol co-evaporation period and ethanol-abundant droplets will undergo an extra ethanol condensation stage after depletion of propellant.