Department of Chemical Technology, University of Calcutta, Calcutta-700 009, India E-mail : achintya_saha@yahoo.com Division of Pharmaceutical Chemistry, Seemanta Institute of Pharmaceutical Sciences, Jharpokharia, Mayurbhanj-757 086, India E-mail : kunalroy_in@yahoo.com Department of Pharmaceutical Technology, Jadavpur University, Calcutta-700 032, India Manuscript received 27 March 2000. revised 25 August 2000. accepted 28 November 2000 Quantitative Structure Activity Relationship (QSAR) analysis of estrogens and non-steroidal analogs of estrogen with electrotopological state atom (ETSA) index has been performed in an attempt to explore the atoms or fragments of the molecules that are most important for the binding affinity to receptor. The study reveals the importance of phenyl ring fragment (C1, C5 and C10 atoms of steroidal estrogen, and C1, C3, C4, C9 and C10 atoms in case of non-steroidal analogs) for receptor binding affinity. The importance of these atoms or fragments is also supported from the literature survey. Thus, the phenyl ring constitutes the pharmacophore for receptor binding affinity of estrogen analogs, Hence, diagnostic potential of the e ETSA scheme in identifying the atoms or fragments important for activity is revealed from the study