Magnetic nickel nanoparticles are prepared by NaBH4 reducing agent in AOT reverse microemulsion, the influence of water content on the morphology and magnetic properties of nickel nanoparticles are investigated by TEM study, size distribution, XRD characterization and magnetization curves. The results show that spherical and polydispered particles are obtained in microemulsion. The dimension and polydispersity of particles increased with the increasing of water content. Magnetization curves clearly indicate a ferromagnetic behavior with high coercivity values. At water content of W0=41.7, the product has a high saturated magnetization 70.68 emu/g with its residual magnetizations 28.02 emu/g, higher than the sample obtained at water content of W0=13.9.