A fluorescent probe 1 for Hg(2+) based on a rhodamine-coumarin conjugate was designed and synthesized. Probe 1 exhibits high sensitivity and selectivity for sensing Hg(2+), and about a 24-fold increase in fluorescence emission intensity is observed upon binding excess Hg(2+) in 50% water/ethanol buffered at pH 7.24. The fluorescence response to Hg(2+) is attributed to the 1:1 complex formation between probe 1 and Hg(2+), which has been utilized as the basis for the selective detection of Hg(2+). Besides, probe 1 was also found to show a reversible dual chromo- and fluorogenic response toward Hg(2+) likely due to the chelation-induced ring opening of rhodamine spirolactam. The analytical performance characteristics of the proposed Hg(2+)-sensitive probe were investigated. The linear response range covers a concentration range of Hg(2+) from 8.0x10(-8) to 1.0x10(-5)molL(-1) and the detection limit is 4.0x10(-8)molL(-1). The determination of Hg(2+) in both tap and river water samples displays satisfactory results.