Nickel oxalate nano-fibers were controlled synthesized via a restricted self-assembly growth process in liquid phase precipitation system. Nickel nano-fibers were prepared by decomposing nickel oxalate under the guidance of fiber micro-structure, in Ar gas atmosphere. The characteristics were measured by the techniques of X-ray powder diffraction, Scanning Electron Microscope and Transmission Electron Microscopy. As a result, the existence of ammonia changed the growth behavior of nickel oxalate from free self-assembly mode to restricted one. The nickel oxalate crystal nano-fibers with monoclinic geometry were about 100-200nm in diameter, 1-5μm in length. The nickel nano-fibers with face-centered cubic geometry were also about 100-200nm in diameter, 1-5μm in length, which surface was very rough. Nickel nano-fibers formed via a process of nucleation, grain growth and aggregation under the guidance of long and narrow space provided by nickel oxalate nano-fibers.