Most of the synthesis paths applied to introduce phosphorus containing moieties into cellulose yield insoluble products due to cross-linking and possess various other shortcomings. Water-free orthophosphoric acid has been used as phosphating agent for preparing cellulose phosphate. For enhancing the reactivity, a mixture of H3PO4 with P2O5 has been employed. Water soluble cellulose phosphates have been synthesized in ternary systems of H3PO4,P2O5 and dimethyl sulfoxide. The reaction of cellulose with a melt of H3PO4 and urea resulted in the formation of a soluble, but strongly degraded cellulose monophosphate monoammonium salt. Phosphorus oxychloride (POCl3) is an effective phosphating agent, starting from cellulose suspension in N,N-dimethylformamide (DMF) or pyridine.