The synthesis and characterization of porous silicon nitride/ silicon carbide nanocomposites have been studied. Porous Si3N4/SiC nanocomposites with 30 and 60 vol.% SiC were fabricated by two sintering steps of the mixture powder of Si3N4, carbon, and yttria Y2O3. The powder mixtures were uniaxially pressed using 25 MPa and sintered in nitrogen gas at 1650, 1750, and 1850oC for 1, 2, and 3 h respectively. The characteristics of porous Si3N4/SiC nanocomposites were investigated by using X-ray diffraction and SEM. Also the compressive strength and microstructure of the Si3N4/SiC nanocomposites were investigated. The strength of Si3N4/SiC nanocomposites depends mainly on the sintering temperature, and the holding time of the sintering. The best holding time for sintering at 1650oC, 1750oC, and 1850 oC are 1, 2, and 3 h respectively.