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Aiming to develop a new generation of lightweight, high-strength, and heat-resistant structural materials, BNNSs/Al composites were fabricated based on powder metallurgy process. TEM results demonstrated that BNNSs were mainly distributed at grain boundaries, forming BNNSs-AlN-Al transition interface during the sintering process. The Al grains of BNNSs/Al composites maintained stable at temperatures up to 573 K and achieved unprecedented high-temperature tensile strength of about 329 ± 6 MPa. The experimental and simulation results revealed that the reduction of tensile strength of Al matrix at high temperature was due to the decrease of grain boundary stability, which led to grain rotation and stress concentration near grain boundary. However, BNNSs with unique two-dimensional morphology can effectively suppress grain boundary diffusion and grain boundary motion, which retarded the softening of …