In this study, in-situ ZrB 2 reinforced 7085 aluminum matrix composites were fabricated via an in-situ synthesis technique. The influence of ZrB 2 nanoparticles on the microstructure and mechanical properties was investigated by optical microscope (OM), scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray diffractometer (XRD) and tensile testing. The results indicate that the strength could be markedly improved by ZrB 2 nanoparticle reinforcement. However, agglomeration of ZrB 2 nanoparticles is aggravated with the volume fraction of ZrB 2 nanoparticles, which is harmful to improving the plasticity and toughness of the composite. Thus, to solve this problem, rare earth elements were introduced into composite materials. The results show that the agglomeration of ZrB 2 particles is improved and the matrix grains are refined significantly. Moreover, the strength and elongation are enhanced. When the volume fraction of ZrB 2 is 2% and mass fraction of Sc is 0.4%, the ultimate tensile strength and elongation of the composite are 534 MPa and 10.2%, respectively, which are approximately17.4% and 14.6% higher than those ofthe 7085 aluminum alloymatrix.