Spinel-Sialon composites were fabricated using magnesite and bauxite as the main raw materials and coke as reductant by carbothermal reduction and nitridation (CRN) in nitrogen atmosphere. The effect of match ratio of raw materials and pre-synthesized temperature on the flexural strength of composites were studied by XRD, SEM and EDS. The results showed that the phases of the fabricated Spinel-Sialon composites were MgAl_2O_4 and Si_3Al_3O_3N_5. The flexural strength of the composite reached a maximum of 239 MPa. The powder pre-synthesized at 1500 ℃ was more favorable for the densification and increasing of the flexural strength of samples than the powder pre-synthesized at 1600 ℃. The apparent porosity of samples decreased and the bulk density and the flexural strength increased with the rising of magnesite amount.