An oxidation bonding process was developed to fabricate oxidation-bonded porous silicon nitride (Si3N4) ceramics from α-Si3N4 powder in air at 1100-1400oC. Si3N4 particles are bonded by the oxidation-derived silica (SiO2) and the pores derive from the stack of Si3N4 particles and the release of N2 and SiO gas during the sintering. The microstructure of oxidation-bonded porous Si3N4 ceramics was observed. Moreover, the fracture mechanism was analyzed. Effects of the bonding phases and pores on the flexural strength were investigated. Oxidation-bonded porous Si3N4 ceramics with high flexural strength was obtained by restraining the crystallization of amorphous silica and forming the well-developed necks between Si3N4 particles.