In this paper, flower-, star-, and chain-like hierarchically nanostructured nickel crystals as well as [Ni(N2H4)2]Cl2 nanorods were first synthesized by a simple reduction method. This method is template-free, environmentally benign, and can be carried out at low temperature (60 °C) with high efficiency on a large scale. Investigation of the growth kinetics has proved that the crystal sizes are sensitive to the reaction temperature and reaction time. Various nickel nanostructures can be achieved by the oriented growth of preferred nickel crystal planes. The magnetic properties of the flower-like nickel nanocrystals were also characterized with the results of much enhanced coercivity (Hc) and decreased saturation magnetization (Ms).