Fluorescence spectroscopy and circular dichroism (CD) spectroscopy were used to investigate the interaction of coumarin-3-carboxylic acid with human serum albumin (HSA) and bovine serum albumin (BSA) under physiological conditions in a buffer solution of pH 7.4. [...] Quenching constants were determined using the Lineweaver-Burk equation to provide a measure of the binding affinity of coumarin-3-carboxylic acid to HSA/BSA. Binding studies concerning the number of binding sites, n, and apparent binding constant, K, were performed by a fluorescence quenching method at different temperatures (298, 303 and 310 K). The thermodynamic parameters, enthalpy change (ΔH0) and entropy change (ΔS0) as calculated according to the van’t Hoff equation, indicated that hydrogen bonding and van der Waals forces play a major role in coumarin-3-carboxylic acid-HSA association whereas electrostatic interactions dominate in coumarin-3-carboxylic acid-BSA association. The distance, r, between the donor (HSA/BSA) and acceptor (coumarin-3-carboxylic acid) has been estimated using Förster’s equation, on the basis of resonance energy transfer. Furthermore, CD spectra were used to investigate the α-helix changes of the HSA and BSA molecules upon addition of coumarin-3-carboxylic acid.