In the present work, we report preparation of NiO nanoparticles with well-defined plate morphology by solid-state reaction of NiCl2∙6H2O and the Schiff base ligand N,N′-bis-(3-methoxysalicylidene)benzene-1,4-diamine), as a novel precursor via solid state thermal decomposition method. This method is a simple and environmentally friendly for preparing transition metal oxides. The result of TGA analysis of the precursor showed that the proper calcinations temperature is 450 oC. The NiO product was characterized by XRD, FT-IR and UV-Vis spectroscopy, SEM and TEM. The results indicated that the obtained product is face-centered cubic of nickel oxide, plate shape with average particle size of 10-20 nm. The optical absorption band gap of the nickel oxide nanoparticles was estimated to be 2.1 eV.