Hybrid AZ91 Mg matrix composites reinforced with ceramic short fiber (Al2O3) and particle (Si or SiCp) were fabricated by squeeze casting method. Microstructure of hybrid Mg matrix was examined and mechanical and fracture properties were characterized. It was found that squeeze casting is effective method for the fabrication of hybrid Mg matrix composites with fairly well distributed reinforcement and near defect-free solidification microstructure. Strength and wear resistance were enhanced with hybridization of reinforcements. To investigate fracture properties of hybrid Mg matrix composites, in-situ micro-fracture experiment was performed in SEM. Crack was initiated and propagated mainly by decohesion of interfaces between Mg matrix and reinforcements. Large ceramic particles tend to fracture and thus seem to be undesirable for mechanical and fracture behavior of hybrid Mg matrix composites.