A detailed scheme of the modification of the hyaluronic acid In the method according to the invention, a pure acylalkyl carbonate is prepared at the temperature of -40 0C to 0 0C, preferably at -15 °C in ether, acetone or dichloromethane, by means of a reaction of the respective carboxylic acid with alkylchloroformate or an analogue thereof wherein the halogen is replaced by another leaving group (substituted quinoline, isoquinoline or 1,2-dihydro analogues thereof). The hyaluronic acid is dissolved in a polar aprotic solvent, preferably in DMSO, followed by the addition of a base, preferably triethylamine, a substituted pyridine, preferably 4 -N,N-dialkylaminopyridine, and finally O- acyl-O'-alkyl carbonates. Then the resulting homogenous mixture is stirred without the access of air humidity at the temperature of 20 to 80 °C, preferably at 20 °C, for 0.1 hour to 96 hours, preferably for 1 hour.