Extracellular vesicles are nanosized lipid-bilayered spheres secreted from every living cell and they serve physiological and pathophysiological functions. Bacterial membrane vesicles are shed from both Gram-negative and Gram-positive bacteria and harbor many virulence factors, nuclear material, polysaccharides, proteins, and antigenic determinants, which are essential for immune recognition and evasion. Hence, bacterial membrane vesicles are very promising vaccine candidates. Spray drying is a well-established pharmaceutical technique to produce inhalable dry powders with enhanced stability for formulations of vaccines. In this chapter, we illustrate general guidelines for spray drying of bacterial extracellular vesicles to improve their stability without compromising their immunogenic protective effect. We discuss some of the most important experiments to characterize the generated spray-dried bacterial membrane vesicle powder vaccine.