Nickel thin films were prepared using electrodeposition process on a copper substrate. The effect of deposition parameters on film microstructure has been investigated with and without an organic additive (saccharin). Electrodeposition has been carried out using direct current electrodeposition (DCED) method and pulsed electrodeposition (PED) method. Significant reduction in crystallite size has been observed with the increase in saccharin concentration (similar to 10 g/L) irrespective of the electrodeposition method. In PED, it has been observed that an increase in pulse width causes a drastic reduction in crystallite dimension (similar to 15 nm) of the deposited Ni-film. Further PED process yielded needle-shaped Ni grains under controlled process conditions unlike in DCED, where spherical grain structure was observed in the micrographs. However, these needle-shaped grains change their microstructure on addition of saccharin to the bath. A phenomenological model is presented to explain the observed microstructural changes.