A new dye chemosensor molecule toward Hg2+ detection based on rhodamine 6G was synthesized by the condensation reaction of compound 2 and 2-amino-5,6-dimethylbenzimidazole. Chemosensor 1 showed highly selective functions toward Hg2+ recognition with compared to other examined metal ions. The chemical structures of all the intermediates and chemosensor 1 were characterized by H-1 NMR, Mass Spectrometer, and elemental analysis. Upon the addition of Hg2+, chemosensor 1 exhibited a remarkable emission change from colorless to green fluorescence. Additionally, the absorption color change from colorless to light pink in UV-vis range was observed. However, other metal ions such as Cu2+, Ag2+, Co2+, Pb2+, Zn2+, Fe3+, Fe2+, and Mg2+ did not accompany any noticeable spectral change.