<p>Lignin phosphorylation is recognized as a chemical modification technique to enhance fire performance as a fire-retardant agent. The isolated lignin from <i>Eucalyptus sp.</i> was synthesized with P₂O₅ to produce phosphorylated lignin. This study aimed to examine the effect of phosphorus supplementation on the properties of phosphorylated Eucalyptus lignin and lignosulfonate. The results indicated that the addition to the mixture enhanced both the yield and purity of phosphorylated lignin compared to phosphorylated lignosulfonate. The phosphorylated lignin contained lignin functional groups, while the phosphorylated lignosulfonate comprised S = O functional groups. Phosphorylated lignin and lignosulfonate exhibit analogous morphologies and retain mineral constituents. Phosphorylated lignin left more ash after burning and had a higher glass transition temperature than phosphorylated lignosulfonate. The equivalent weight and S/G ratio of phosphorylated lignosulfonate are greater than those of phosphorylated lignin. The ¹³C NMR results from the phosphorylation process showed major changes in the structure of lignin and lignosulfonate. Phosphorylated lignin showed modifications to the side chain and aromatic system. On the other hand, phosphorylated lignosulfonates showed a major reduction in all functional groups, particularly methoxy and phenolic-OH groups, indicating that their structure was more extensively broken down.</p>