Abstract: Human β₂ microglobulin （β₂ m） is a low molecular weight protein （MW 11,600） and has been purified from the 24-hour urine of patients with kidney transplantation. The urine protein was first precipitated with ammonium sulphate （50g/160ml）.The procedure for its isolation and purification included G100 gel chromatography and ion exchange chrotography,using DEAE₅₂ cellulose. The purified protein appeared homogeneous in cellulose acetate membrane electrophor- esis and SDS-PAGE.The moleular weight determined by SDS-PAGE was 12,000.