Development of simple, sensitive and selective detection probe for Hg(II) ions in natural water is still achallenge to the researchers due to stringent and permissible limits set by World Health Organization(WHO). Herein, highly selective optical (absorbance and fluorescence modes) sensing probe for moni-toring Hg(II) ions in synthetic urine and ground water has been successfully demonstrated using goldnanoparticles (AuNPs)/rhodamine B (RB)/hexanedithiol (HDT) nanocomposites system. The incorpora-tion of RB and HDT on AuNPs improved sensitivity and selectivity (1.8 times) towards Hg(II) ions overother metal ions, respectively. The proposed mechanism involved in Hg(II) sensing in absorbance modewas based on aggregation of composites AuNPs, while fluorescence mode was based on the turn on flu-orescence approach through release of RB from AuNPs/RB/HDT nanocomposites system via subsequentformation of Hg-HDT complex. The linear dynamic range for detection of Hg(II) ions using AuNPs/RB/HDTnanocomposite system, when tested in optimized colorimetric and fluorescence based analytical methodadopted to the Hg(II) spiked urine and ground water samples exhibited detection limit of 1 ng mL⁻¹(1 ppb) and 0.5 ng mL⁻¹(0.5 ppb) using absorption and fluorescence mode, respectively, which weresignificantly comparable to those used in other developed Hg detection probes.