Quantum-dot cellular automata (QCA) is a new nanotechnology which facilitates computation paradigms with extremely low energy dissipation. In this paper, a novel efficient full adder–subtractor in QCA nanotechnology is proposed. First, one bit full adder with minimum delay cell is designed. Then the proposed full adder is used to design an efficient full adder–subtractor with minimum number of cells. The proposed circuit does not need any rotated cells and only uses one layer. Therefore, manufacturability of the design significantly improves. In addition, our design achieves 44 cell in full adder and only 83 cell in full adder–subtractor. The proposed full adder–subtractor only occupies 0.09 µm² area.