Glutathione transferase is one of the important enzymes for xenobiotic metabolism. Glutathione transferases catalyze the conjugation of various electrophilic endogenous and exogenous xenobiotics with -glutamyl-cysteinyl-glycine (GSH). GST activity can be changed by natural plant products. The present study's goal is to examine the interaction of human erythrocyte GST with the natural plant compounds baicalin, baicalein, phloridzin, and phloretin. First, GST was purified from human erythrocyte with 1654-fold purification and 19.27% recovery by glutathione agarose affinity chromatography. The purity of the enzyme was checked by SDS-PAGE, showing single band, because it had a homodimer structure. Baicalin, baicalein, phloridzin, and phloretin flavonoids were shown to inhibit human erythrocyte GST with the IC50 values of 28.75, 57.50, 769.10, and 99.02M, respectively. The K-i constants for baicalin, baicalein, phloridzin, and phloretin flavonoids were 14.50 +/- 0.71, 24.33 +/- 2.08, 762.50 +/- 85.97, and 86.49 +/- 1.11M, respectively. According to these results, baicalin is the best inhibitor for human erythrocyte GST.