In digital IC designing, energy dissipation has already become a crucial factor that is taken into consideration. Since irreversible computing is one of the most significant cause of energy dissipation, designing digital circuit by reversible logic is an efficient way to decline the energy dissipation of the circuit. While BCD encoder is one of the most common unit circuits, existing BCD encoders are all designed in irreversible way. Thus we propose a new design of BCD priority encoder by reversible logic. This revised encoder not only resolves the problem of messy codes, but also declines certain amount of energy dissipation by utilizing reversible logic.