Abstract: In order to adapt the demands for the lightweight of materials, MgAl₂O₄-CaAl₄O₇-CaAl₁₂O₁₉ (MA-CA₂-CA₆) composite was developed at 1 400-1 600℃ by addition of La₂O₃ micro powder, and the effect of La₂O₃ addition on sintering behavior, microstructure and mechanical properties of the composite was discussed. The results show that the added La₂O₃ dissolves to the CA₆ phases of MA-CA₂-CA₆ composite, causing the lattice distortion of CA₆ crystal, and the abnormal grain growth rate of CA₆ to be decelerated, resulting in a more equiaxed morphology instead of anisotropic growth to platelet structure, thereby further contributes to the elimination of pores located between the initial plate-like CA₆ grains. The disappearance of the platelet structures is favorable to Mg²⁺ diffusion and thus indirectly promotes the development of MA grains, so the sintering activity of MA-CA₂-CA₆ composite is comprehensively promoted. As a result, the dense microstructure is obtained, with the apparent porosity decreases from 19.2% to 6.1% and the bulk density increases from 2.78 g/cm³ to 3.18 g/cm³ after presintering at 1 200℃ and sintering at 1 600℃ for 2 h by addition of 4wt% La₂O₃. In addition, a texture microstructure of the crystal phase, which includes MA, CA₂ and CA₆, is observed in the typical back-scattered electron (BSE) images of microstructures with 4wt% La₂O₃ content La₂O₃/MA-CA₂-CA₆ composite samples sintered at 1 600℃ for 2 h, which is considered to be favorable to improve the mechanical properties of MA-CA₂-CA₆ composite, and the cold compressive strength increases from 317 MPa to 501 MPa after presintering at 1 200℃ and sintering at 1 600℃ for 2 h by addition of 4wt% La₂O₃.