Nonlinear optical properties of phenyl/-NH2 end-capped tetraaniline in dimethyl sulfoxide solutions were investigated as a function of the tetraaniline concentration for both doped and undoped samples. We employed the single beam Z-scan technique with 70-ps-duration pulses at 532 nm, in association with others complementary techniques such as UV-vis absorption spectroscopy and time-resolved fluorescence. Our results show that both the nonlinear refractive index and the nonlinear absorption diminish for the doped sample, following the same behavior of the absorption coefficient.