In the electrodeposition of Ni-P alloy from a Ni-citrate bath, changes in P content and current efficiency of Ni-P deposits with plating variables such as H2PHO3 concentration, current density, bath pH and temperature were investigated. P content of the deposits was found to be constant around 25 at.% in a wide range of plating conditions. It was concluded that Ni-P alloy electrodeposition is controlled by Ni deposition rate and by the strong interaction between P and Ni, and that Ni-P alloy is formed through a direct deposition mechanism.