Spin mixing conductance (SMC) at the ferromagnetic/non-magnetic material (FM/NM) interface governs the transport efficiency of the spin current. A high level of SMC is crucial for efficient spin injection and spin manipulation. Here, we report a reliable way to enhance the SMC at the FM/NM interface by rare-earth doping in the NM layer. As evidenced by the decreased saturation magnetization in permalloy (Py)/Cu–Nd structures, an induced magnetism in Nd is proposed, which is likely to be antiferromagnetically coupled to Py at the interface. By changing the doping content of Nd, the Py/Cu–Nd interface can be well designed, which gives rise to an effective tuning of the SMC from 0.37 × 1015 to 16.26 × 1015 cm−2. Such a tuning effect of SMC is suppressed by inserting a Cu spacer, demonstrating the key role of the antiferromagnetically coupled interface to the improved SMC. Our results highlight the significance of rare-earth materials in spin transport, expanding the design capability of energy-efficient spintronic devices.