In this paper, the electronic structure of chemisorption of CO on Rh(lll) surface (θ≤l/3) has been calculated by the method of the self-consistent Hartree-Fock-Slater molecular cluster. The variation of the energy levels and total energy with respect to the vertical distance of the CO molecule above this surface is obtained. The optimized bond distance determined from the total energy curve is 1.85 ?, which is quite close to experimental result 1.95±0.1?. The binding energy is 0.98 eV, which is smaller than the experimental adsorption energy of 1.3 eV. The total density of states with above bond distance is calculated and it is in good agreement with the UPS result considering final state and relaxation effect. The bonding and antibonding character for the CO valence level have also been studied by analysis of the variations of the molecular eigenvalues when the CO molecule approaches the surface. The charge transfer for CO chemisorption on transition metal Rh is investigated through a Milliken population analysis and the analysis of coefficients of cluster wavefunction which is expanded by using CO molecular wavefunction. This charge transfer causes the activation of absorbed CO molecules.