Silver nanoparticles were prepared by a green method using Cordia myxa leaf extract. They were characterized by UV-Vis spectroscopy, FT-IR spectroscopy and their XRD pattern. Their sizes were determined by SEM, TEM imaging and DLS analysis. The shapes of nanoparticles were spherical or trancated triangular and their average size was determined to be 51.6 nm. Their solution was stable for more than 9 month with no aggregation and their zeta potential (-28.3 mV) confirmed this stability. The prepared silver nanoparticles were used as chemical sensor for determination of iron(III) and mercury(II) ions with detection limits of 0.084 nM and 0.037 nM respectively. It was shown that the mechanism of these detection is through oxidation of Ag atoms by Fe3 and Hg2 ions.