<,正,>, The fully oxidized state of polyaniline （PANI）, pernigraniline （PN）, was synthesizedby oxidation of the emeraldine base form of PANI dissolved in NMP solvent with m-chloroperoxybenzoic acid. The resulted PN was characterized by FTIR and UV-Visiblespectra. The third-order nonlinear optical properties of PN in concentrated sulfuric acid（PN/H,2,SO,4,） were measured by a degenerated four wave mixing （DFWM） method. The re-sults obtained suggest that the soliton-pair intermediate state associated with thedegenerated state does not play a major role in the third order nonlinear optical prop-erties of PANI.