Abstract-Reversible quantum computer is the best choice for the future computer system. With the advent of quantum computer and reversible logic, design and implementation of all devices has received more attention. BCD digit adder is the basic unit of the more precise decimal computer arithmetic. Several proposals have been given for the BCD adders. This paper proposes a reversible implementation of 2:1 vector MUX and a combined BCD Adder / Subtractor. This paper can be extended to execute more complex operations using reversible logic.Index Terms-BCD adder-subtractor, decimal arithmetic, reversible logic, quantum computer, low-power VLSI