Vapor-phase adsorption of acetone and n-hexane by different carbon nanofibers (CNFs) was investigated. Two kinds of CNFs with different pore size distributions were fabricated by the two syntheses: thermal chemical vapor deposition and template-assisted synthesis. Langmuir and Dubinin-Radushkevich models were employed to estimate the surface accessibility to adsorbates and the mean energy during the adsorption. It was suggested on the basis of the present work that the surface area and micropore fraction of the CNFs are important factors in determining the adsorption capacity. Both the equilibrium constant and free energy for adsorption are favorable for the CNFs with the mesopore fraction, indicating that the presence of mesopores facilitates the adsorption to high-energy sites.