Nanoparticles of metal and other materials are a proven reinforcing material for producing a high-performance aluminum composite utilized in modern engineering applications. The ultrasonic mixing process is conducted to ensure a typical distribution of nanoparticles in the aluminum matrix. The present work aims to study the effect of copper nanoparticles on microhardness and physical properties of Al-composite prepared by powder metallurgy techniques with ultrasonic mixing. The aluminum nanocomposites were fabricated with different volume fractions (0, 5, 10, 15, 20, and 25 wt%) of Cu nanoparticles. To examine the effectiveness of the mixing, compacting, and sintering process, nanocomposites were characterized using field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray (EDX) and elemental mapping analysis. A uniform distribution of Cu nanoparticles was established within the Al matrix. The composite was characterized by an increase in density and a decrease in porosity with increased Cu nanoparticles. Increasing Cu nanoparticles enhanced the mechanical properties of the Al-Cu composite through an increase in its hardness. A direct relationship between Cu nanoparticles and thermal and electrical conductivity was found; in particular, there was a distinct enhancement in electrical conductivity, as the composite with 25 wt% Cu nanoparticles reached 78.87% of the electrical conductivity of pure Cu.