Abstract Circularly polarized 129 keV γ-rays from oriented 191mIr nuclei are used to measure the Compton profile of magnetic electrons in ferromagnetic iron. A high degree of circular polarization is obtained even at temperatures about 200 mK owing to the large hyperfine magnetic field at the Ir site in Fe metal. Utilization of a 40 mCi γ-ray source, together with a 3He/ 4He dilution refrigerator and a solid state detector, is found to be effective in obtaining high statistical accuracy. Efficient geometrical arrangement of the apparatus is discussed based on the cross section of the spin-dependent Compton scattering. Experimental procedures, source preparation and data accumulation are described in detail.