In this work, the Al2O3/Ti3SiC2 composites with different Nb doping amounts (0-5 vol%) were prepared by vacuum hot pressing sintering (30 MPa, 1450 for 1 h). Various tests and characterization had been performed on samples to investigate the dependence of Nb doping on the mechanical properties and microstructure of Al2O3/Ti3SiC2 composites. Nb doping can optimize the microstructure of Al2O3/Ti3SiC2 composites. Scanning electron microscopy (SEM) images showed that with the increase in Nb doping, the pores of the composites gradually decreased and the microstructure became denser. Based on X-ray diffraction (XRD) pattern analysis, it was found that Ti3SiC2 may react with Nb to form the enhanced phases Ti5Si3, TiC and Nb3Si. Therefore, with the continuous doping of Nb, more toughening phase Ti3SiC2 will be converted to the strengthening phases, leading to the sacrifice of partial fracture toughness to improve the bending strength and hardness of Al2O3/Ti3SiC2 composites.