Response of aging treatment on aluminum alloy towards its hardness has been investigated. Alloy used on this research was develop base on a US patent 4121951 that is use to produce aluminum cable with excellent strength and conductivity . Solutioninzing treatment was carried out to the alloy at 520 °C for 2 hours. Alloy then were artificial aged at 180 °C, 200 °C and 220 °C for various periods up to 10 hours. Natural aging also has been carried out for 2 weeks right after solution quenching. By referring to the results, hardness increase as the aging time increase until it reaches the maximum peak and then decreases as the result of overaging. Hardness of artificial aged alloy then was compared with 99.99% pure aluminum, as-cast and naturally aged alloy. Alloy aged at 180 °C for 2 hours give the highest value of hardness which is 34.26 Hv followed by naturally aged alloy and pure aluminum with 30.92 Hv and 15.2 Hv. The effect of different time of artificial aging gives significant change in hardness in order to improve the strength of aluminum alloy. Minor addition of zirconium during the aluminum processing will probably cause by the precipitation of Zr particles towards the aluminum matrix , thus increase the strength even these particulate cannot be detected by XRD. These particles will retard the grain movement and also stable upon heating due the low solubility of zirconium in aluminum matrix.