Glutathione S-transferase ρ (EC 2.5.1.18) has been purified to homogeneity from human erythrocytes. A combination of gel filtration, ion exchange and hydroxylapatite chromatographic procedure yields the specific activity of 20.8 units/㎎. The purified enzyme gives a single band corresponding to 24,000 M.W. on a sodium dodecyl sulfate polyacrylamide gel electrophoresis. The enzyme molecule is characterized to be an acidic protein (pI 4.6) having a dimeric structure with 48,000 M.W. composed of identical size of polypeptide chains. Apparent K_m and V_(max) were determined to be 1.1 mM and 1.0 mmol/1/min for 1-chloro-2,4-dinitro benzene respectively while 0.3 mM and 0.55 mmol/l/min for glutathione. Results obtained from chemical modification studies suggest that essential amino group(s) critically connected to the catalytic function of glutathione S-transferaseρ.