Estrogenic transformation products (TPs) generated after water chlorination can be considered as an environmental and health concern, since they can retain and even increase the estrogenicity of the parent compound, thus posing possible risks to drinking water safety. Identification of the estrogenic TPs generated from estrogenic precursor during water chlorination is important. Herein, butylparaben (BuP), which was widely used as preservative in food, pharmaceuticals and personal care products (PPCPs), was selected for research. A simplified effect-based analysis (EDA) approach was applied for the identification of estrogenic TPs generated during BuP chlorination. Despite the removal of BuP corresponds to the decrease of estrogenicity in chlorinated samples, an significant increase of estrogenicity was observed (at T = 30 min, presented an estrogenicity equivalent to 17β-estradiol). Chemical analysis of the estrogenic chlorinated samples that have been previously subjected to biological analysis (in vitro assays), in combination with the principal component analysis (PCA) evaluation, followed by validating the estrogenic potency of most relevant estrogenic TPs through an in silico approach (molecular dynamics simulations), identified that the halogenated TP3 (3,5-Dichloro-butylparaben) increased by 62.5 % and 61.8 % of the estrogenic activity of the parent compound in samples chlorinated with 30 min and 1 h, respectively being classified as a potentially estrogenic activity driver after BuP chlorination. This study provides a scientific basis for the more comprehensive assessment of the environmental and health risk associated with BuP chlorination, highlighting the necessity of identifying the unknown estrogenic TPs generateded from estrogenic precursors chlorination.