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In this study, polymerization mechanisms of aromatic (C6H5 or C6F5) and alkyl (CH3, C2H5, C3H7, C6H13, C12H25 or C18H37) amine based naphthoxazine monomers (15-Na, 15Na-C1, 15Na-C2, 15Na-C3, 15Na-C6, 15Na-C12 and 15Na-C18) and thermal degradation mechanisms of polynaphthoxazines synthesized by curing the naphthoxazine monomers (P-15-Na, P-15NaF, P-15Na-C1, P-15Na-C2, P-15Na-C3, P-15Na-C6, P-15Na-C12 and P-15Na-C18) were studied by direct pyrolysis mass spectrometry. During the curing process, the evolutions of monomer and low mass aromatic or alkyl amines were detected below the curing temperature. The mass spectrometry findings indicated that the monomers were subjected to evaporation and degradation to a certain extent but also to polymerization during the curing process. It has been determined that the polymerization of aromatic amine based naphthoxazine monomer proceeded through the aniline units, either by coupling of the radicals produced by the ring opening of the side chains or by substitution to the benzene ring of aniline. However, even if no direct evidence to confirm polymerization by attack of &ndash / NCH2 groups to naphthalene ring was detected, it is not possible totally eliminate its existence. The evolution of aniline, the main thermal degradation product for this polymer was observed at relatively low temperatures indicating that thermal decomposition started by elimination of aromatic amine involving linkages. Coupling of &ndash / CH2 groups generated by loss of aniline, yielded naphthoxazines with unsaturated linkages that can recombine and form a crosslinked structure with higher thermal stability. Similarly, the polymerization of naphthoxazines based on alkyl amines followed opposing paths. The mass spectral data indicated that the coupling of alkyl amine radicals was the main polymerization pathway. Again, thermal decomposition of alkyl amine based naphthoxazines was started by loss of alkyl amines and diamines. The crosslinked structures produced by coupling of the radicals generated by lose of alkyl amines decomposed at relatively high temperatures.