The adsorption isotherms of water and ethanol by fluorinated activated carbon fiber (F-ACF) and ACF were determined. Water was not completely adsorbed by F-ACF until P/P-0 = 0.8, regardless of micropore volume of 0.21 mL g(-1), while the water adsorption isotherm of ACF rose steeply above P/P-0 = 0.4. The amount of water adsorption by F-ACF at P/P-0 = 0.9 was less than 1/50 of that by ACF. However, the amount of adsorption by F-ACF was more than a half of that by ACF. Fluorinated carbon micropores were presumed to repel water almost completely without formation of water molecular clusters.