Polarized absorption spectra of a 2-naphthoic acid single crystal and those of a 2-naphthoic acid in diphenyl mixed crystal have been studied at 90 K in the region of the first absorption system. From both these studies it has been found that the transition moment for the first absorption system of 2-naphthoic acid is developed along the short axis if the molecule. But the first electronic transition of naphthalene is long axis polarized. Thus the substitution of a carboxyl group in the 2 position greatly affects the electronic spectrum of naphthalene.