Sodium citrate is a useful setting retardant for improvement of properties of brushite cement. Sodium citrate monobasic (Sodium dihydrogen citrate) is the monosodium salt of citric acid. Isopiestic method has been proposed for the evaluation of vapor-liquid equilibrium parameters (water activity, vapor pressure, osmotic coefficient and activity coefficient) for the binary aqueous mixtures of sodium dihydrogen citrate. X-ray diffraction method has been reported to investigate the crystal structure of sodium dihydrogen citrate. Its crystals are monoclinic having space group of P21/a.