The purpose of this study was to determine the crystallisation behaviour of the two sugar alcohols mannitol and sorbitol and stability thereof after spray-drying aqueous solutions of mannitol/sorbitol-mixtures (ranging from 10 to 40% of sorbitol in the formulations). By means of Differential scanning calorimetry and X-ray powder diffraction the effects observed in melting behaviour and crystal structures as consequences of spray-drying and storage conditions were investigated. Using Near-Infrared spectroscopy it was possible to take a closer look at the polymorphism of each compound. Neither co-crystals nor eutectic mixtures were obtained. The components crystallise separately. Concerning sorbitol mainly a solidified melt is harvested, besides some amorphous material, which transforms into the β- and α-modification during storage. Mannitol was determined to crystallise as β-mannitol accompanied by little amounts of the α-polymorph. This constellation turned out to be stable. The co-spray-dried formulation was extremely sensitive to increased humidity.