Al-based immiscible systems, such as Al-RE (rare earth), seem to be promising materials for high conductivity conductors as RE alloying elements have zero solubility in Al and thus are less detrimental for electrical conductivity. The intermetallic phases, precipitated as small particles and uniformly distributed in the alloy's volume, may significantly increase the mechanical strength and thermal stability of alloy. However, the immiscible element compound concentration should be controlled as an excessive amount might result in a loss of electrical conductivity. Therefore, the optimization of RE concentration to obtain the best combination of mechanical strength and electrical conductivity is considered in this research. It focuses also on the effect of high-pressure torsion (HPT) and post deformation annealing temperature on mechanical and electrical properties of Al-RE (La + Ce) alloy. Alloys with total Ce and La concentrations of 2.5, 4.5 and 8.5 wt % are subjected to HPT at room temperature and subsequent annealing in the range of temperatures 230–400 °C. The optimal concentration of RE and processing parameters for enhancement of both mechanical strength and electrical conductivity are defined.