In the present study, an acidic palladium-nickel alloy plating solution was prepared with ethylenediamine as the complexing agent, and the physical properties of the alloy plating layer were investigated. The palladium-nickel alloy plating layer could be deposited over a broad range of current densities as the deposition potential of palladium in the solution containing ethylenediamine significantly shifted toward the base direction and the value was similar to that of nickel. X-ray diffraction patterns confirmed that the palladium-nickel alloy existed as a single-phase solid solution in the prepared alloy. The hardness of the palladium-nickel alloy plating layer increased with the increase in nickel content. The surface and cross-sectional images of the palladium-nickel alloy plating layer indicated a dense and uniform morphology without defects such as cracks and pores.