High particle content B₄C/Al composites reinforced with different particle sizes were fabricated. Based on the tensile and compressive stress–strain behaviors of these composites, the effective medium approach was employed to investigate the load partition behaviors between the matrix and reinforcement. The results showed that the load borne by the particles increased in compression, which lead to larger compressive strength than the tensile strength. Meanwhile, the load borne by particles increased with decreasing particle size during compression. These observations were rationalized based on the combined theories of geometrically necessary dislocations and metal-based cemented granular material behaviors.