Chemical phosphorylation of hyaluronic acid (HA) remains an unresolved problem for the chemistry of this unique polysaccharide, since convenient phosphorylating reagents are not reactive enough to obtain HA phosphates (HA-P) with a satisfactory degree of esterification of hydroxyl groups. The synthesis of phosphates of low molecular weight (43 kDa) and high molecular weight (0.5–0.7 MDa) HA was undertaken by us using such reagents as sodium trimetaphosphate Na₃P₃O₉, H₃PO₄, NaH₂PO₄/Na₂HPO₄, and anhydride P₂O₅. Solid-phase HA esterification with P₂O₅ was found to be the most convenient and efficient method. The HA-P samples were characterized by XRF and NMR spectroscopy (³¹P and ¹H-³¹P) and contained, depending on the HA/Р₂О₅ ratio, 0.30–6.25% P wt. in the form of disubstituted mono-, di- and polyphosphates.