We employed a polyaromatic hydrocarbon C54H18 as a model cluster for disordered carbons and investigated the effect of BNB-unit substitutions on the electronic and Li absorption properties of disordered carbons, by using a semiempirical molecular orbital method. BNB substitutions prefer to occur at the periphery of C54H18 Sheet and create electron acceptor levels in a lower energy region than that for C54H18, This level accepts electrons from the absorbed Li atoms more easily, so that the Li absorption energies for these BNB-substituted C54H18 are larger than that for C54H18 The absorbed Li atoms are stabilized near B atoms to be far from N atoms, and (BNB)(2)-substituted C54H18 has smaller Li absorption energy than B2C52H18. These results; indicate that N atoms may have a negative effect for enhancing Li-absorption energy of disordered carbons.