A new method of calculating molecular orbitals and orbital energy levels of biomolecules is proposed based on the fragment molecular orbital method (FMO), in which a huge biomolecule is first divided into 'fragments' for feasible calculation. In the present method, called FMO-LCMO, one-electron Hamiltonian of the whole molecule is derived from the output of FMO with little computational cost. The method gives fast and accurate description of the molecular orbitals of the whole system by a linear combination of molecular orbitals (LCMO) of the fragments and provides a good starting point for understanding the electronic structure of biomolecules. (C) 2009 Elsevier B.V. All rights reserved.