Spray drying has become not merely a drying process, but also an important tool for engineering solid structures, specially for multi-component feeds. In that way, it is important to know how the drying conditions and liquid formulations affect the particle final solid structure. In the present study, we investigated the changes on the solid structure of a spray-dried binary mixture of lactose and whey protein isolate under different process and formulation conditions. Particle morphology, diameter, porosity and occluded air were analyzed. Total solid content in the feed was the parameter of highest impact on the spray-dried particle’s occluded air volume.Keywords: spray drying; solid structure; porosity; hollow particless.