In this work, the fundamental mechanisms for ceramic particle deformation in aerosol deposition were investigated. We hypothesized that pre-existing defects affect ceramic particle deformation under compression. Preliminary results showed that near defect-free, sub-micron, single crystal alumina (Al2O3) particles exhibited dislocation nucleation and motion along with significant plastic deformation, shape change, and cracking in compression at room temperature. In contrast, highly defected, micron-sized alumina particles exhibit no observable change in shape before fracture and fragmentation. Particle deformation mechanisms, identified through this work, provide insight into feedstock design for solid state alumina deposition using the aerosol deposition process.