A rhodamine-based sensor RB-S2 was designed and synthesized by combination of the thiospirolacton chromophore and the thiophen ring block with high affinity to Hg(2+). Probe RB-S2 exhibits high selectivity and excellent sensitivity in both absorbance and fluorescence detection of Hg(2+) in aqueous solution. In addition, fluorescent imaging of Hg(2+) in MCF-7 cells is also successfully demonstrated.