The sintering additive used in SiAlON containing 5, 20, 15 and 20 eq% Al was a concentrate of rare earth elements, with 89.5% Y2O3, 3.9% Er2O3, 3.8% Dy2O3, 1.8% Lu2O3 and other rare earth elements at lower concentrations. The sintering variables studied were: Al content in solid solution with SiAlON, heating rate, sintering time and temperature. The results show that an increase in Al concentration leads to higher densities and alpha --> beta transformation, and smaller grains with more spherical shape. An increase in both sintering time and temperature and heating rate lead to the formation of larger grains with smaller aspect ratio. Samples sintered at 1700 degrees C/30 min had higher density values. Samples with 99% of theoretical density were obtained by using the concentrate of rare earth elements.