The work is devoted to the chemical modification of the natural chitosan polymer to improve its quality and suitability for further use in chemical processes. Chitosan samples with an increased degree of deacetylation and a reduced molecular weight were synthesized by the purification with sodium hydroxide with subsequent re-precipitation. Additionally, the chitosan succinate, chitosan hydrochloride, and thyoled chitosan were obtained. These compounds are characterized by solubility in a wider pH range compared to the commercially available samples. For each of the synthesized samples, infrared diffusion reflection spectra were obtained. The modified samples of chitosan were used for obtaining nanoparticles and finely-dispersed films.