The reaction sequences of formation of different SiAlON phases along the Si3N4-Y2O3.9AlN.AlN-Al2O3 concentration plane in the Y-Si-Al-O-N system have been studied through dilatometric investigations. The presence and stability of some crystalline phases greatly influence the nature of the liquid, which ultimately go,, erns the sintering process. Detailed knowledge of the sintering of different phases is useful to highlight a useful compositional zone where good densification of the multiphase SiAlON ceramics may be achieved.