The x-ray diffraction measurements of n-propanol adsorbed on graphite have been taken over the temperature range 90-250 K and the coverage range 1.34-4.17 molecule/nm(2). The diffraction pattern clearly illustrates that a two-dimensional smectic liquid crystal is formed in a melting process of an anisotropic, incommensurate monolayer of n-propanol on graphite. In this phase a hydrogen-bonded head-to-head association of molecules is arranged in lamellae with their long axes on average normal to the lamella. The results are compared with the theory based on the unbinding of dislocations.