Sodium hexametaphosphate (Na-HMP) is a common liquefying agent widely used in the ceramics industry for modifying the rheological behavior of ceramic slurries. The objective of this study was to investigate the influence of Na-HMP on several properties of calcium phosphate cements (CPCs). Various types of CPCs were prepared by mixing the same powder, namely, a mixture of tetracalcium phosphate and dicalcium phosphate anhydrate, with various liquids, namely, distilled water, Na(2)HPO(4) solutions, and Na-HMP solutions. The setting time, mechanical strength, rheological properties, and injectability of the cement pastes were examined in this work. Also, X-ray diffractometry (XRD) and scanning electron microscopy (SEM) techniques were employed for phase analysis and morphological evaluations, respectively. The results showed that, compared to CPCs made with water and Na(2)HPO(4) solutions, the CPC pastes made with Na-HMP solutions had improved stability and injectability but prolonged setting times. The XRD and SEM studies showed that Na-HMP inhibited the growth of apatite crystals during soaking of the cements in Ringer's solution. Thus, the CPC made with Na-HMP solution had lower compressive strength than those made with water or Na(2)HPO(4) solutions. Although Na-HMP could improve the injectability and stability of the CPC paste, it impaired other basic properties of the cement. Thus, it is not an appropriate liquefier additive.