A novel topological index based on Wiener index, named Lu index, is proposed and can be used for modeling properties of hetero-atom-containing and multiple bond organic Compounds. The usefulness of the Lu index was demonstrated by modeling normal boiling points and molar refractions of aldehydes and ketones, and the retention indices or gas chromatography of hydrocarbons and halogenated hydrocarbons. The high correlation coefficients (>0.99) for all constructed models indicate the need of such an index, and show the potential of the Lu index for QSAR/QSPR studies. (c) 2005 Elsevier B.V. All rights reserved.