High selectivity and fluorescence sensitivity of a well-recognized antiexcitotoxic and anticonvulsant drug, kynurenic acid (KA), toward Cd-II ion has been demonstrated by UV-vis, fluorescence, H-1 NMR spectroscopy in combination with computational calculations. Upon complexation with Cd-II, KA exhibits a distinct excimer emission at 528 nm along with monomer emission at 402 nm. The sensing ability of drug KA toward Cd-II ion is distinctly different from sensing for Hg-II or Cu-II ion. KA can form dimer by intermolecular O-H center dot center dot center dot O hydrogen bonding between the -COOH groups. Presence of Cd-II metal ions promotes dimer formation in the excited state which exhibits excimer fluorescence. (C) 2014 Elsevier B.V. All rights reserved.