Ramified fractal structures of nickel chloride have been observed experimentally using vapour deposition. Each fractal pattern consisted of numerous long crystals which stacked together in a regular order and formed a self-similar structure on a ceramic substrate during the phase transition. These structures were strongly dependent on the surface roughness of the deposit substrate. No fractal pattern forms on a mirror-face substrate. The experimental results show that a nucleation-aggregation (NA) model can be used to explain well the self-assembly at the vapour-solid interface.