Mannitol is one of the excipients widely used in the pharmaceutical industry and approved for pulmonary administration. Recent studies have indicated that polymorphism of carrier particles is one of the possible important factors affecting the performance of DPI formulations. Therefore, for the development of carrier particles for DPI formulation, controlling the polymorph of a carrier particle is considered an important issue. Previously, we developed a manufacturing method for producing a metastable α-mannitol by co-spray-drying mannitol aqueous solution combined with polyethylene glycol (PEG). The aim of this study was to evaluate the aerosolization performance and physical stability of co-spray-dried mannitol (co-SDM) with PEG as a carrier particle candidate in a DPI formulation. As results of stability studies of co-SDMs with PEG confirmed, the α-mannitol was stabilized during storage when an adequate amount of PEG was added. The molecular weight of PEG little affected the physical stability of mannitol as long as an adequate amount of PEG was added. It was considered to be important to reduce the mobility of mannitol molecules by adding PEG to the co-SDM to stabilize the α-mannitol in the co-SDM. As results of in vitro deposition studies further confirmed, as carrier particles, co-SDM particles with 5% PEG 4000 showed the superior aerosolization performance to that of commercial β-mannitol. The polymorph of carrier mannitol particles may be shown to be one of the factors that will increase the aerosolization performance. Co-SDM particles have shown to be the promising candidate as a carrier particle for DPI formulation.