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 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/P2O5 ratio, 0.30–6.25% P wt., in the form of disubstituted mono-, di-, and polyphosphates.