A novel colorimetric and ratiometric ligand based on azo dye 4-(4-Dimethylamino-phenylazo)-N-pyridine-2-ylmethyl-benzamide (L) was synthesized in high yield and was carefully investigated. The sensing activity of the ligand toward different cation ions was studied. The ligand demonstrated a highly selective colorimetric sensing toward Fe3+ in acetonitrile aqueous solution with a detection limit of 1.8 × 10-8 M. The developed ligand showed a visual color change from yellow to red with naked-eye, a very effective way to identify Fe3+ instead of spectroscopic instrumentation. In contrast, no color change was observed in the presence of other ions. In addition, the ratio of metal-ligand interaction, determined by Job’s plot method, was 1:1. Furthermore, cation binding character was determined using visual inspection, UV–vis, fluorescence, and 1H NMR analyses. In addition, interactions between the receptor and Fe3+ ion were investigated by spectroscopy and DFT computational studies. The theoretical study showed that oxygen and nitrogen atoms of L are coordinated as a bi-dentate ligand in the L-Fe3+ by making sevenmember rings.