The conjugated polymer P-1 could be synthesized by the polymerization of 4,7-diethynyl-benzo[2,1,3] thiadiazole (M-1) and 1,4-bis[3'-(N,N-diethylamino)-1'-oxapropyl]-2,5-diiodobenzene (M-2) via Pd-catalyzed Sonogashira reaction. The water-soluble conjugated polyelectrolyte P-2 could be obtained by the reaction of P-1 with ethyl bromide. Both P-1 and P-2 can emit orange fluorescence. The responsive optical properties of P-1 and P-2 on Hg2+ were investigated by fluorescence spectra. Hg2+ can lead to nearly complete fluorescence quenching of P-1. On the contrary, Hg2+ can show the most pronounced fluorescence enhancement response of P-2 in aqueous solution without interference from those coexistent ions, such as K+, Mg2+, Pb2+, Co2+, Ni2+, Ag+, Cd2+, Cu2+, Fe3+ and Zn2+. The results also exhibit that this kind of water-soluble conjugated polyelectrolyte can be used as a highly sensitive and selective fluorescence sensor for Hg2+ detection in water. Crown Copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.