Morphology control is one of the major aspects associated with the preparation of fine powders for the particle design of dry powder inhaler (DPI) formulations. We used betamethasone (BMZ) as the model steroid drug for DPI formulations and sodium surfactin (SF-Na) as the biosurfactant to modify the surface of the BMZ particles. Two types of BMZ particles with different crystal states, which exhibit different morphological properties, can be obtained using the spray-drying and freeze-drying method. The aerosol dispersion performance of the formulations measured using an Andersen cascade impactor revealed that the fine particle fractions of the BMZ/SF-Na (4/1) SDPs and FDPs are 53.4% ± 4.7% and 17.1% ± 3.4%, respectively. High aerosol performance of the BMZ spray-dried formulation may be achieved using SF-Na because the presence of SF-Na on the surface of the formulation plays an essential role in aggregate prevention. The results indicate that biosurfactant-assisted morphological control may be used to obtain fine particles for efficient pulmonary delivery. Display omitted •Bio-surfactant improves the dispersion of inhaled BMZ formulations.•The presence of SF-Na may inhibit the crystallization of BMZ.•Morphology and surface of BMZ powders was modified with SF-Na.•BMZ spray-dried particles with SF-Na could be achieved to deeper lung position.