Investigations of a range of glass ceramic compositions have been developed in the last decades. These materials show a good potential to be used at room temperature as a substitute to other ceramic materials, due to their lower sintering temperature and costs. The mainly reason that limits the use of these materials is their low mechanical strength. In this work a Li2O-ZrO2-SiO2-Al2O3 (LZSA) glass powder was mixed with 30 wt. % of ZrO2 or Al2O3 (submicron size), uniaxially pressed under 40 MPa and sintered at 650 ºC/30 min. In some samples a second sintering step at 1000 ºC during 30 minutes was also performed, in order to improve the mechanical properties by increasing the crystallized fraction. The sintered samples were characterized by bending strength measurements, X-ray diffraction and scanning electron microscopy analyses. Apparent densities values were determined by the Archimedes's method. The results obtained in this work indicate that the addition of ZrO2 and Al2O3 (reinforcing particles) decreases the density of the glass-ceramic materials. X-ray diffraction analysis indicated an increase of the crystallized fraction in samples sintered at 1000 ºC. Fracture strength values has showed to be dependent on the sintering temperature and also on the reinforcing crystalline particles.