A TEM investigation on the orientation relationship of α-Co precipitates in a copper matrix has revealed that these f.c.c precipitates, approximately 15-20 nm in diameter, were formed in Cu 7 0 Co 3 0 ribbons during melt-spinning. After annealing at 573 K, these precipitates grew to about 30-50 nn in diameter. Analysis of selected area diffraction patterns (SAPD) combined with the dark field imaging technique confirms that the orientation relationship between these α-Co precipitates and the Cu matrix is not a cube-cube relationship, but a twin-type one, i.e, {111} C o //{111} C u and 110 C o // 110 C u .