Chitosan (degree of deacetylation of 90.2%) and N‐carboxymethylchitosan (N‐CMCh) (degree of substitution of 18.5%) were analyzed using thermogravimetric analysis in order to determine their thermal stability. Also, their films were evaluated using scanning electron microscopy (SEM) and mechanical and dynamic mechanical analysis (DMA). Both polymers showed a thermal degradation peak at Tm ∼ 250 °C, with Tonset and weight loss of 175 °C and 62% and 190 °C and 35% for chitosan and N‐CMCh, respectively. N‐CMCh showed a second thermal degradation peak at Tm = 600 °C, with an additional weight loss of 25%. Kinetic thermal analysis showed a slower process of degradation at 100 °C for N‐CMCh compared with chitosan, and an activation energy 13 times higher for the former, confirming the higher stability of N‐CMCh. Analysis of chitosan and N‐CMCh films showed that the latter support a high tension, with lower elasticity, and, as revealed by DMA, N‐CMCh has a more compact film structure, with a crossing arrangement of N‐CMCh fibers, as compared with the chitosan films which were determined from SEM analysis to have fibers in one direction only. Copyright © 2006 Society of Chemical Industry