Fractal pore-size distribution K(x) is given based on J(x) function proposed by Jaronic. Activated carbon fibers (ACF) with different surface areas are characterized by using two functions mentioned above. The present work studies the fractal pore-size distribution of ACF and adsorption isotherms of nonpolar benzene vapor on ACF, and thereby reveals the correlation between them. Fractal pore-size distribution K (x) is given based on J (x) function proposed by Jaronic. Activated carbon fibers (ACF) with different surface areas are characterized by using two functions mentioned above. The present work studies the fractal pore-size distribution of ACF and adsorption isotherms of nonpolar benzene vapor on ACF, and so reveals the correlation between them.