Mullite based ceramics were prepared by reaction sintering of mixtures containing kaolin clay and kaolin waste. Phase composition, apparent density, apparent porosity, and modulus of rupture were investigated as a function of sintering temperature and kaolin waste content (varied from zero to 50 wt%). The sintering shrinkage behavior was monitored by dilatometry. The results showed that samples derived from formulations containing kaolin waste were composed of acicular mullite and glass phases at 1500 °C. Ceramic bodies prepared with kaolin waste (25 or 50 wt%) showed better physico-mechanical properties (for sintering up to 1400 °C) than the ones of pure kaolin clay. The evidence seems to suggest that this behavior can be due to a liquid phase assisted sintering mechanism associated with a content of mica ranging from 13.3 to 22.4 wt%