The spin reorientation from the <111> to the <100> easy-magnetization axis as a consequence of the competition between the cubic magnetocrystalline anisotropy constant K 1 0 and the magnetoelastic contribution to the magnetic anisotropy ΔK 1 m e was predicted and observed upon magnetic dilution of the uranium sublattice of UFe 2 . The total K 1 =K 1 0 +ΔK 1 m e was determined from the magnetization measurements on single crystals of UFe 2 and U 0 . 8 Lu 0 . 2 Fe 2 as -0.21 and 0.15 MJ/m 3 (at 4.2 K), respectively. The individual values of K 1 0 and ΔK 1 m e in UFe 2 were found as 1.03 and -1.24 MJ/m 3 , respectively, which shows that the low magnetic anisotropy of UFe 2 is a result of the mutual cancellation of rather large K 1 0 and ΔK 1 m e . The change of the anisotropy type is accompanied by the disappearance of spontaneous magnetostriction distortion in U 0 . 8 Lu 0 . 2 Fe 2 .