Spray forming was employed to refine the microstructures to improve the workability of AZ91 Mg alloys. The process parameters of spray forming were varied to reduce the porosity level and improve the morphology of the billet preforms. As-spray-formed microstructures were characterized, which were compared with as-cast microstructures. In the workability study, cylinder specimens were extruded by simple direct extrusion with various ram speeds at various temperatures. Surface conditions and microstructures of extruded materials, and extrusion pressure vs. ram displacement were analyzed. The effects of extrusion temperatures and ram speeds on the workability of spray-formed and cast materials were studied and compared. The extrusion operating conditions of spray-formed and cast materials were determined.