N-substituted carboxyl polyaniline (NPAN) is readily prepared through chemical oxidative polymerization of N-phenylglycine in hydrochloric acid solution. Techniques such as Fourier transform infrared spectroscopy, 1H-NMR spectrometry, UV–vis spectrophotometry, and X-ray diffraction are employed to characterize the structure of the prepared NPAN. The 1H-NMR spectra indicate that the ratio of the aromatic protons to methylene protons in pristine NPAN chains is 4:1, which suggests that only a –CH2COONH4 group remains after both monomers react. Elemental analysis experiments demonstrate that the benzene rings in the polymer backbone transfer into the quinone units through a process of decarboxylation during the polymerization. The solubility of NPAN in most polar solvents is outstanding in comparison with that of polyaniline, and NPAN exhibits solvatochromic properties in different solvents. Moreover, the conductivity of NPAN changes in the range of 4.7 × 10−3 S×cm−1 to 1.49 × 10−1 S×cm−1 as the acidic medium in the reaction system is changed. The minimal temperature of the derivative thermogravimetry curve is shifted to a substantially higher temperature by approximately 186 °C in the case of pure NPAN. The thermogravimetric analyses reveal that pure NPAN exhibits better thermal stability than polyaniline.