Commercial purity aluminum was reinforced with different percentages of carbon nanohorns (CNH) using ball milling (1 h) followed by spark plasma sintering (SPS) at 550 °C for 5 min under 50 MPa pressure with heating rate 100 °C/min. The microstructure, hardness and compression properties of the spark-plasma-sintered carbon-nanohorns-reinforced aluminum (Al-CNH) composites were evaluated. Transmission electron microscopy revealed a uniform distribution of 0.3% CNH in Al, but above 0.3% CNH, agglomeration occurred. The compression strength of Al-0.3%CNH composites increased by 44% compared to the milled Al sample without CNH. © 2020, ASM International.