Fracture behaviour and mechanical properties are the key features when a material for given application is supposed to be selected. Advanced glass ceramics composites are perspective structural materials for many applications due to their low production expenses and satisfactory properties even at elevated temperatures. Borosilicate glass matrix composite reinforced by alumina platelets was investigated to describe toughening mechanisms and their changes in a wide range of temperatures (from room temperature up to glassy transition temperature Tg). The dissipation of energy by bridging and/or deflection of propagating crack by alumina platelets uniformly dispersed in the glass matrix were the main toughening mechanisms observed. The alumina platelets have a higher ability to deflect propagating crack in comparison with spherical or rectangular particles having the same volume. Three and four point bend test for Young’s modulus and flexural strength determination was used. Fracture toughness determination was conducted using chevron notch technique. More than 100% increase of fracture toughness was observed when 30% of alumina platelets were added in to borosilicate matrix.