In this investigation, five aluminum matrix nanocomposites were obtained by the hot pressing at 800 MPa and 600 ^oC. The electrolysis coating technique was utilized to prepare the nano-nickel powder. The fabricated nanocomposites were characterized by studying their chemical composition, microstructure, hardness, and thermal expansion coefficient. The scanning electron microscope of the microstructure of the electroless nickel powder shows that the Ni particles have nano-size where it was less than 100 nm. The EDAX analysis of the fabricated composite that contains 25 wt. % (Al₂O₃) in different regions was established. No elements rather than Al, Cu, Ni, and O were observed. The hardness of the aluminum matrix increases as the content of the Al₂O₃ increases. In addition, the thermal expansion coefficient was reduced by increasing the Al₂O₃ content for reasons related to the low thermal expansion of the alumina reinforcement 7.2 x10^-6 mm/^oC compared with aluminum that has 23.1x10^-6 mm/^oC.