Vanadyl phthalocyanine (VOPc) thin films are fabricated using molecular beam epitaxy (MBE) technique on KBr (001) substrate preheated at different temperatures under vacuum. VOPc thin films on the KBr substrate cleaved in air and then preheated in vacuum are investigated using scanning electron microscopy (SEM) images and UV-vis absorption spectra. VOPc thin films depend upon preheating temperature of KBr substrate. Large VOPc grains appear in the background of small crystals on the substrate preheated at low temperatures, while more small grains appear on the substrate preheated at higher temperatures and the film is smoothly and epitaxially grown. The preheating at high temperatures removes adsorbed gasses from the substrate. The effecs of preheating indicate that gas molecules adsorbed on the KBr substrate strongly affect the morphology of the VOPc thin film. The third-order nonlinear optical susceptibilities χ⁽³⁾ (-3ω; ω, ω, ω) of the epitaxial and pseudomorphic VOPc films were determined using the Maker fringe technique.