Oxidation of ethanol has been performed over CsnH4-n PMo11VO40 (0 less than or equal to n less than or equal to 4) catalysts in order to investigate the oxidation property of acidic Cs salts of molybdovanadophosphoric acid. A flaw-type packed bed reactor was used for the reaction. Acetaldehyde was produced by oxidation catalysis, while ethylene and diethyl ether were produced by acid catalysis. The yields of these products were strongly dependent on the amount of Cs contained. Acid catalysis was dominant in n < 3, especially 2.5 < n < 3; this could be explained by high surface acidity caused by high surface area and uniformity. On the other hand, oxidation catalysis was remarkably improved for n greater than or equal to 3. For these catalysts, acetaldehyde was produced selectively and the yield increased up to 38%, which was three times higher than that of n < 3. Several characteristic studies using XRD, ESCA, ICP, solid-state NMR, and CO2 adsorption have showed that the high oxidation activity for n greater than or equal to 3 was attributable to the increased surface basicity caused by surface Cs species being not, incorporated into the bulk structure.