The full alkali concentration range phase diagrams of the Na2O-Al2O3-H2O system were constructed at (150 and 180) degrees C. The compositions of the clear liquids and wet solid phases were analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES), and the results show that, as the Na2O concentration increases, the Al2O3 solubility initially increases monotonically, to maximum values of 100 w (mass fraction) = 33.58 and 35.86 at (150 and 180) degrees C, respectively, and then decreases. At both temperatures, the solid phases were determined to be Al2O3 center dot H2O, Na2O center dot Al2O3 center dot 2.5H(2)O, Na2O center dot Al2O3, and NaOH by X-ray diffraction coupled with Schreinemaker's method. The phase diagrams indicate that, as the temperature increases, the Na2O center dot Al2O3 center dot 2.5H(2)O phase region shrinks, while that of the Na2O center dot Al2O3 phase expands.