To measure the concentration of Ag+ cation in solutions, a new optical chemical sensor was fabricated by covalent immobilization of Thiazole yellow dye on a triacetyl cellulose film via a linker, called epichlorohydrin. The interaction between the Ag+ cation and immobilized Thiazol yellow molecules was investigated using UV-Vis spectrophotometry. The fabricated optode indicated a range from 3×10 -7 to 2.5×10-5 M regarding to the concentration of Ag+ cation at pH 6 and the detection limit was searched to be: 0.8×10-7 M. The constructed optical chemical sensor, shows a long-term stability, good reproducibility and repeatability,and also satisfied selectivity and sensitivity. The sensor response to Ag+ cation is absolutely invertible and it can be reproduced simply with a solution of EDTA (ethylenediamine tetra acetic acid) in about 5 minutes. The response time is 10 minutes. The fabricated optode can be employed successfully to determine the concentration of Ag+ cation in actual sample solutions.