This study investigates interaction of glycyrrhizin (an herbal therapeutic agent) with human haemoglobin. The interaction is confirmed by glycyrrhizin-induced quenching of absorbance and fluorescence data. Both hydrophobic and electrostatic interactions appear to be involved in glycyrrhizin-haemoglobin binding. The binding causes no change in the secondary structure of haemoglobin. The interaction decreases H2O2- induced iron release from haemoglobin and haemoglobin- mediated oxidative reactions. Glycyrrhizin inhibits ferryl-haemoglobin formation, peroxidase and esteraselike activities of the heme protein. Almost no oxygen is released from haemoglobin due to glycyrrhizin binding. The interaction thus reduces haemoglobin-mediated oxidative damage without affecting oxygen-binding capacity of the protein, and may be an advantage in therapeutic application of glycyrrhizin.