The effect of aluminum on the precipitation hardening of Cu-Ni-Zn alloys with varying aging temperatures and times was investigated in this article, in the hope to achieve better mechanical properties. Vickers hardness, tensile, and electrical conductivity tests were carried out to characterize the properties of the Cu-Ni-Zn alloys with or without an addition of aluminum subjected to different aging treatments. The results show that an addition of 1.2 wt% aluminum can play an influential role in the precipitation hardening of the Cu-Ni-Zn alloys. For example, it can increase the peak hardness from 58 Hv for the solution-treated Cu-10Ni-20Zn alloy to 185 Hv for the solution-treated Cu-10Ni-20Zn-1.2Al alloy during aging at 500 degrees C. The yield strength, tensile strength, and electrical conductivity of the Cu-10Ni-20Zn-1.2Al alloy subjected to suitable treatments under prior cold-rolled and aged conditions can reach 889 MPa, 918 MPa, and 10.96% IACS, respectively, being much higher than those of the relevant alloy without aluminum and comparable to those of the Cu-Be alloys (C17200 and C17510). According to the transmission electron microscope observations, it was found that formation of nanosized precipitates with the L1(2)-type ordered lattice results in precipitation hardening, and an orientation relationship of [011](p)//[011](m) and (100)(p)//(200)(m) exists between the precipitates and the alpha-Cu matrix.