The effect of water content in the precursor solution on thermal stability in the preparation of Sr-hexaaluminate was examined by XRD, SEM, TEM, BET and XPS analysis. Large water content caused a rapid decrease in the surface area of hexaaluminate. XPS analysis also showed enrichment of the element when large amount of water was added during the hydrolysis step. This result implies that the addition of large amount of water affected the surface properties of hexaaluminate; the instability of the unbalanced surface composition as compared with bull; composition, accelerated the sintering phenomena which resulted in the rapid particle growth and drastic decrease of surface area.