In this study electrodeposition of nanocrystalline nickel coating, using direct current was performed in Watts type bath. The effect of current density on grain size, texture and morphology of the nanocrystalline nickel coating was investigated. In addition, using electrochemical impedance spectroscopy (EIS), adsorption phenomena at different current densities and its effect on nickel deposition mechanism have been studied. The effect of pH, coating thickness, and saccharin addition have been investigated, too. Results obtained revealed that, at low current densities in modified Watts bath, physisorbed atomic hydroge inhibits growth and therefore decrease the grain size. Increasing the coating thickness to 12 micron, does not affect the coating texture. Variation of pH did not have any effect on grain size. The domain at which hydrogen adsorption proceeds from nickel reduction, was detected by getting derivate from charge transfer resistance against potential. By increasing the current density, the texture of coatings changed from (220) A at low, to (200) at medium and to (220) B at high current densities. The grain size was decreased by saccharin addition. However, charge transfer resistance was increased by saccharin additions which means that surface diffusion coefficient of adsorbed nickel ions on substrate surface was decreased and therefore nucleation rate was increased ( i.e. inhibited growth effect ). On the other hand, the texture intensity at the presence of saccharin was weaker and consisted of two components of (111) and (200).