The sintering behaviour of β-Si3N4 powder was investigated in 980 kPa (10 atm) nitrogen at 1800–2000 °C. It is shown that β-Si3N4 has a higher sinterability than the finer α-Si3N4. The solution of small grains and reprecipitation on large grains occurred during sintering at >1600 °C. The rate-determining step in the liquid-phase sintering is believed to be the diffusion of material through the liquid phase at grain boundaries. There was no abnormal grain growth during gas pressure sintering of β-Si3N4. The microstructures of gas pressure sintered materials from β-Si3N4 were more uniform than those from α-Si3N4. The densification mechanism of β-Si3N4 is discussed in relation to that of α-Si3N4.