 This is the first study to report the synthesis of porous nickel phosphide (NiP) thin films with one-dimensional nano-pore channels via a porous template-free, single-step plating process. The nano-pores in the synthesized films were primarily formed in areas where multiple grain boundaries met during the island growth of three-dimensional grains. We investigated the factors that affect pore formation by considering the electroplating reaction mechanism of nickel phosphide and the pattern of grain growth over time, and we determined that grain size and gas generation were the dominant factors affecting pore density. Grain size and gas generation can be adjusted by altering the plating conditions, such as current density and electrolyte pH; we have demonstrated that by controlling these conditions, the pore density can be controlled in an expected manner.