Phosphorylated chitins (P-chitins) as the additives of calcium phosphate cements (CPCs) were prepared by thephosphorylation of chitin with phosphorus pentoxide in methanesulfonic acid. Their physical properties and effects on CPCsfrom monocalcium phosphate monohydrate (MCPM) and calcium oxide (CaO) or dicalcium phosphate dihydrate (DCPD)and calcium hydroxide [Ca(OH)2] were investigated. Addition of P-chitin (Mw = 2.60 x 104; degree of substitution, DS =0.68)to the liquid phase in amounts up to 3 wt% for MCPM and CaO cements or 1.5 wt% for DCPD and Ca(OH)2 cementscould enhance the mechanical strength considerably, while little influence on the setting time was observed. However, furtheraddition of P-chitin will cause no setting.