Castable machinable glass-ceramics have been widely considered as aesthetic materials for dental restoration. In order to extend their applications to bridge-work fabrication, it is necessary to increase their fracture strength and fracture toughness. The effects of ziconia and alumina additions on the properties of glass-ceramics, especially on the mechanical properties were studied. It was found that appropriate addition of alumina increases the bending strength due to aluminium strengthening the glass-ceramic by means of incorporation into the glass network. However, additions of ziconia fail to show promising results on the mechanical property. The evolution of recrystallization and the associated microstructure were also studied and are discussed.