Quantum Cellular Automata (QCA) provide a new computing paradigm to implement the high speed digital architecture at nano-scale with low power consumption. The design of an 8-bit arithmetic logic unit (ALU) for microcontroller using QCA technology is the most challenging and has not been addressed so far. In this paper, we propose a systematic design approach for the design of novel energy-efficient 8-bit ALUs for scalar microcontrollers using QCADesigner. The proposed eight-bit ALU uses 24.25 (10-1ns) clock delay, occupies 198.48 µm2 area, and dissipates 15.5 eV of energy.