Al2O3·SiO2f/A356 composites contained La were fabricated by squeeze casting, and effect of La on the solute segregation and microstructure were researched. The results indicate that the microstructure in the composite can be refined by La, which enriches near the interface to be favorable to improve the wettability between the fiber and Al alloy. The phases RE-richening do not formed at the interface. There is no special influence of La on the Mg segregation in the matrix alloy. The distribution of Mg and La in the composite are near the interface.