Abstract: A specific and sensitive optical chemical sensor (optode) was fabricated for the determination of mercury ions. The optode was prepared by recently synthesized composites, 5, 10, 15, 20-tetrakis (4-hydroxyphenyl) porphyrin (THPP) that stabilized with graphene oxide nanosheets. The graphene oxide–porphyrin composites were synthesized and characterized by field emission scanning electron microscopy (FE-SEM), UV-Vis and Fourier transform infrared (FT-IR) spectroscopic techniques. By interacting the mercury ions and the membrane phase, Hg2+-ionophore complex forms and causes a change in the absorbance of the sensor. A decrease in absorption of the membrane at 426 nm could be used as a suitable wavelength for quantitative determination of Hg (II). The various experimental parameters such as pH of aqueous solution of Hg (II) and content of the THPP as well as the grapheme oxide have been optimized. This optode exhibits a linear range of 6.0×10-5 to 6.0×10-9 mol.L-1 Hg(II) with a detection limit of 3.2×10−9 mol.L−1 and a response time of ∼210 s. Performance characteristics of the sensor evaluated such as good reversibility, selectivity, wide dynamic range, long life span, and high reproducibility. The optical sensor was successfully applied to determination of Hg (II) in water samples.