We report a simple strategy for the fabrication of a highly selective and sensitive Hg(II) chemosensor based on HMS-Ag composite functionalized rhodamine derivative (R). The prepared chemosensor HMS-Ag-R was characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), UV-vis spectrum and Fourier transform infrared spectroscopy (FT-IR). HMS-Ag-R has both fluorescence and colorimetry performance, and it can realize onsite and real-time detection of Hg(II) with a high sensitivity (0.7 ppb) in aqueous solution. In high concentration of mercury ions, the fluorescence intensity of HMS-Ag-R against Hg(II) sufficiently showed a typical sigmoidal shape. Moreover, HMS-Ag-R presents excellent anti-disturbance ability when exposed to a series of competitive cations such as Ag(I), K(I), Li(I), Na(I), Ba(II), Ca(II), Cd(II), Co(II), Cu(II), Mg(II), Mn(II), Ni(II), Pb(II) and Zn(II). It can be applied to the determination of Hg(II) in aqueous media. The interaction between HMS-Ag-R and Hg(II) could occur in a short time (90 s). Importantly, HMS-Ag-R could be regenerated with tetrapropyl ammonium hydroxide (TPAOH) solution.