The structures and melting of n-butanol and n-pentanol monolayers adsorbed on graphite have been studied by x-ray diffraction. The structures of both monolayers change between partial and complete monolayers. The complete monolayer of butanol, as well as the partial monolayer of pentanol, take herringbone structures similar to those of butane and hexane monolayers and have zigzag chains of hydrogen bonds. Two-dimensional smectic liquid crystals are formed in melting processes of the complete monolayers of both molecules while the partial monolayers melt directly into liquids. In the mesophases their solid structures ate essentially maintained. The results are compared with those of the monolayers of shorter linear-chain alcohol molecules and the effect of molecular length on the melting behavior is discussed.