The density-functional theory (DFT) for molecular fluids [J. Chem. Phys. 115, 6653 (2001)] is extended to the case of polymer liquids. A system consisting of the ideal chains is employed as a reference system for the DFT, where many-body effects are considered as an effective field that acts on each site of the ideal chains. We derived a relation between the site-site pair distribution functions and the site-density distribution functions under a mean field arising from a single polymer molecule. An integral equation for the site-site pair distribution functions is obtained by the DFT, where the external field is taken to be the mean field. We propose an approximate expression of the intramolecular correlation functions for isolated single-polymer chains to take account for the excluded volume effects inside a polymer chain. The intramolecular correlation function considering the excluded volume effects was in qualitative agreement with those obtained from a simulation for liquid consisting of freely jointed tangent-soft-core chains. The site-density integral equation under the mean field, using the intramolecular correlation function, reproduces the simulation results for site-site pair distribution functions of the system of freely jointed tangent-soft-core chains. (C) 2003 American Institute of Physics.