The benzaldehyde-ammonia titration (BAT) method clarified that the tungsta impregnated on zirconia formed a monolayer and almost completely covered the surface with ca. 4 W nm(-2). Generation of acidity on the monolayer was shown by the water vapor treatment method of ammonia TPD (temperature-programmed desorption). Strength of the acid site was calculated according to the theoretical equation to be ca. 130 W mol(-1) in adsorption heat of ammonia, which does not correspond to superacidity. The generated acid site was active for skeletal isomerization of butane.