Herein, a fluorescence sensor based on the fluorescence quenching phenomena was developed by the functionalization of Pyranine molecules over the surface of carbon nanotubes (Pry-CNTs) for quick, selective and sensitive detection of Fe3+ ion. The change in the emission along with the Fluorescence Quenching response was found linearly comparative to the Fe3+ ion concentration in the range of 0.1 - 10 mu M, with the limit of detection of 0.2 mu M. The Fluorescence study proved the coordination interaction between Fe3+ ion and Pry-CNTs lead to the recognition process. The developed fluorescence sensor is the simple and selective link for the determination of Fe3+ ion. The recovery of this method in the determination of Fe3+ ion in real water samples was found to be 99.5-100 %. This fluorescence sensor (Pyr-CNTs) can be used as a sensor for Fe3+ ion and promote for many applications in the environmental, chemical and biological systems.