Whisker or particle reinforced magnesium matrix composites were fabricated by squeeze casting process, compo casting process and infiltration technique. Aluminum borate (Al18B4O33) whisker and particles is good reinforcement of AZ91D magnesium alloy because of low reactivity between reinforcement and matrix during the fabrication process. Squeeze casting process is suitable for partial strengthening of magnesium products. The mechanical properties of this composite improved dramatically by isothermal forging after casting. On the other hand, magnesium alloy infiltrate quickly to All 8134033 whisker preform in reductive atmosphere without pressure, so that the composites can fabricated easily. Compo casting process is suitable technique for fabrication of the composites because of low combustibility and oxidation for magnesium alloy. These composites have good mechanical properties by hot-extrusion and semi-solid forming.