Abstract: This invention relates to a novel method of preparation of hyaluronic acid derivatives by means of a reaction of the hyaluronic acid with the complex (O-acyl-O?-alkyl carbonate-substituted pyridine) of the general formula R—CO—O—CO—O—R1 and R25C5N. The reaction takes place in DMSO in the presence of an external base, forming O-acylated products. The method leads to higher substitution degrees and shorter reaction times compared to the known analogues, hi case the agent comprises two or more functional groups R(CO—O—CO—O—R1)n, crosslinked hyaluronic acid derivatives are formed.