The effect of shape and volume percent of Mo particles on the flexural strength and fracture toughness of MgO-Al2O3-SiO2 (MAS) glass/Mo composites was investigated. The flexural strength and fracture toughness of composites depends heavily on Mo particle shapes, and there is greater improvement in composites reinforced with flaky rather than massive Mo particles. In the composites reinforced with flaky Mo particles, fracture toughness increases with volume percent of Mo and, at 50 vol% Mo, is 11.6 MPa root m, which is approximately 6.7 times higher than that of the matrix. Increases in fracture toughness of composites reinforced with flaky Mo particles is greater than with SiC whiskers, SiC platelets, SiC particles or ZrO2 particles. Fabricating composites reinforced with flaky Mo particles is an effective toughening technique capable of simultaneously improving the strength and toughness of brittle materials, such as monolithic Al2O3 and MAS glass, by utilizing plastic deformation of ductile phase.