Tetrafluorophthalonitrile reacted readily with nucleophilic reagents such as methanolic potassium hydroxide, aqueous ammonium hydroxide or dimethylamine. In all cases, the fluorine atom of 4-position was replaced first, and 3, 5, 6-trifluoro-4-methoxy-, 3, 5, 6-trifluoro-4-amino- and 3, 5, 6-trifluoro-4-dimethylamino-phthalonitrile were obtained. Tetramethoxyphthalonitrile was obtained if an excess methanolic potassium hydroxide was used. The structures of these products were determined by ¹⁹F and ¹H nmr spectra.