Abstract: The tautomerism between enol and inone forms of 1-phenylazo-2-naphthol is discussed in this work. The density functional theory (DFT) method is used at the level of B3LYP/6-31+G(d,p) for computations and it showed good agreement with the experimental data qualitatively. Generally quinone forms (of studied compounds) are more stable than naphthol forms. Electron attracting groups move the equilibrium also towards quinone form while releasing groups move the equilibrium to the naphthol form. The polarity of solvents does not have significant effect on the equilibrium.