Nitrate is one of the major environmental problems in today ’s world, which affect human health and welfare, and hinders the sustainable development of both society and the economy. Therefore, the growth of sensor based on decorated noble metal nanoparticles (NPs) such as Ag have been attracted great attention for their convenience of simple operation, excellent absorption and scattering (extinction) properties in recent years. A new and simple fluorometric sensing probe based on polyaniline functionalized AgNPs for NO3- ion detection was developed by polymerization method. It has been successfully synthesized by in- situ polymerization method. The structural and optical properties of the as- synthesized nanocomposites were characterized by using, Fourier- Transform Infrared spectroscopy (FT-IR), powder X-ray diffraction (XRD), Photoluminescence (PL) and UV-Vis spectroscopy. In the absence of nitrate ion, the PANI/Ag exhibit high fluorescence intensity. Yet, the strong coordination of the basic sites with nitrate ion, causes fluorescence intensities quenching through static quenching leading to the qualitative and quantitative detection of nitrate ion. Factor affecting the detection system such as pH and concentration are optimized. Also, the developed PANI modified Ag sensor exhibits high selectivity and sensitive toward nitrate ion with detection limit of 8.9 x 10-4 M. The practical use of the sensor as well tested by spiked with different concentration of nitrate ion solutions on cabbage samples. The result signposted a good linear relation between FO/F and the spiked concentrations of nitrate ion with coefficient of regression R2 = 0.991 (n= 3) and also confirms that the found values is agreed well with the spiked amount.