Proton-free, alkali-containing layered metal oxides are thermally stable compared to their protonic counterparts, potentially allowing catalysis by Lewis acid sites at elevated temperatures. However, the Lewis acidic nature of these materials has not been well explored, as alkali ions are generally considered to promote basic but to suppress acidic character. Here, we report a rare example of an unusually acidic cesium-containing oxide CsxTi2-yMyO4 (x = 0.67 or 0.70; M = Ti vacancy square or Zn). These lepidocrocite-type microcrystals desorbed NH3 at >400 degrees C with a total acidity of less than or similar to 410 mu mol g(-1) at a specific surface area of only 5 m(2) g(-1), without the need for lengthy proton-ion exchange, pillaring, delamination, or restacking. The soft and easily polarized Cs+ ion essentially drives the formation of the Lewis acidic site on the surfaces as suggested by IR of sorbed pyridine. The twodimensional layered structure was preserved after the oxide was employed in the ethanol conversion at 380 degrees C, the temperature at which the protonic form could have converted to anatase. The structure was also retained after the NH3 temperature programmed desorption measurement up to 700 degrees C. The production of ethylene from ethanol, well-known to occur over acid sites, unambiguously confirmed the acidic nature of this cesium titanate.