The effects of temperature and hydrogen partial pressure on porous nickel morphology during the low-temperature (T<500°C) reduction of bulk nickel oxide were studied. It was shown that during the reduction process of nickel oxide at 300°C in an atmosphere of pure hydrogen nickel metal thin plates assembled into bundles and separated by cracks were formed. Increasing the reaction temperature up to 500°C led to a significant change in the morphology of the metal and formation of a porous cellular structure with a mesh size of about 0.1-0.2 μm. Decrease of hydrogen partial pressure led to growth of metal mesh cells and transition from the plate-like to the cellular morphology at 300°C. It was shown, that both increasing the surface diffusion of metal atoms and decreasing the surface reaction rate led to a change from the plate-like to the cellular morphology and the growth of the cell size.