A sinter-bonding method for a typical structural ceramic, Si3N4, has been studied by making good use of 3Y-ZrO2/Al2O3 composites powder as an interlayer. During the process of the sinter-bonding, the sintering of the inserted powder as well as the bonding of the interfaces, Si3N4/ inserted powder /Si3N4, progressed imultaneously. Since superplasticity in the 3Y-ZrO2/AlO3 composites can arise after, even during, the sintering process under proper bonding temperature and stress conditions, the surface roughness of the Si3N4 to be bonded can be filled up mainly by the material flow of the interlayer even though the surfaces are uneven and have curvatures. It was found that the sinter-bonding of the polycrystalline Si3N4 specimens was completed at temperatures ranging from 1573 to 1813 K with bonding stresses ranging from 4 to 10 MPa, at which superplastic flow of the inserted material would arise, whereas the Si3N4 showed no permanent deformation. The bonded Si3N4 specimens showed the bending strength of more than 300MPa at room temperature.