Quantum-dot cellular automata (QCA) is a novel nano-electronic technology. QCA has attracted wide attention due to its extremely small feature sizes at the molecular or even atomic scale and ultra-low power consumption, making it a promising candidate to replace the complementary metal oxide semiconductor (CMOS) technology. Binary-Coded Decimal (BCD) adders are widely used in industrial computing. In this paper, we propose two types of excess-3 code (XS-3) based BCD adders (XS-3DAs). We use ripple-carry adders (RCA) and parallel binary adders (PBA) to construct XS-3DAs in QCA Designer tool, respectively. The PBA-based XS-3DA is constructed with a new correction logic. 4-bit, 8-bit, and 16-bit XS-3DAs are constructed based on the two proposed XS-3DAs, respectively. Comparisons show that, with the increase of design scaling, the delay and area-delay product (ADP) of the PBAbased XS-3DAs can be significantly reduced in comparison with that of the RCA-based XS-3DAs. Compared with the 16-digit RCA-based XS-3DA, the cell count, area, delay and ADP of the proposed 16-digit PBA-based XS-3DA are reduced by 37.88%, 25.99%, 37.68% and 53.88%, respectively.