Detection of mefenamic acid (M, non-steroidal anti-inflammatory drug, NSAIDs) and its metallodrug was investigated using electrospray ionization mass spectrometry (ESI-MS) and fluorescence spectroscopy. ESI-MS data (500 µL, 1× 10-3 M) revealed high detection sensitivity for the drug and metallodrug. ESI-MS spectra revealed peaks at 242, 580, and 777 Da corresponding to [M+ H]+,[63Cu (MH) 2 (H2O) 2+ H]+, and [56Fe (MH) 3+ H]+, respectively. The metal: mefenamic ratios of ESIMS spectra are in complete agreement with the fluorescence spectroscopy results (1: 2 for Cu (II) and 1: 3 for Fe (III)). ESI is a soft ionization technique that can be used on labile metallo-mefenamic acids and is promising for the detection of these species in environmental samples and biological fluids.