Aluminum composites containing Ni in their composition are limited. The low solubility of nickel in the aluminum results in the formation of different phases during solidification. For the amount of nickel less than 40 wt.%, Al3Ni is the most probable phase which can form in Al-Ni system. In this study different amounts of nickel were added to A356 aluminum alloy. Then, the microstructure of the composites was studied using scanning electron microscopy. Primary α-Al and Si besides a third phase in the microstructure are detected phases. For phase characterization, XRD and EDS analysis was performed to evaluate the third phase and the presence of Al3Ni phase was observed. The presence of Ni in the composition of the composite disappeared Al/Si eutectic and in the presence of 6 wt.% Ni α-Al/Al3Ni eutectic was observed. Moreover, the study of the mechanical properties of the composites containing different amounts of nickel (from 6 wt. % to 12 wt. %) showed that the presence of Al3Ni decreases the room temperature tensile properties of the A356 alloy.