The magnetic properties of initial and heat treated Co 69 Fe 4 Cr 4 Si 12 B 11 microwires in a glass shell with the diameter D = 125 μm and the diameter of the amorphous metallic core d = 90 μm produced by the Ulitovsky-Taylor method have been studied. It has been found that the magnetic characteristics, in particu lar, the saturation field H S and the coercive force H C of the samples annealed at a temperature T < 300°C do not differ from H S and H C of the initial microwire, and those of the samples annealed at T ≥ 400°C increase by almost one order of magnitude. The obtained experimental data have been explained by the structural fea tures of the microwires. The near surface values of H S and H C at T < 300°C are found to be larger than the bulk values by a factor of 5-10. These experimental data have been explained by the existence of structural and chemical ingomogeneities in the near surface layer, which are inherent in amorphous materials. This dif ference decreases with a further increase in the annealing temperature, but H S and H C increase substantially. This fact has been explained by the beginning of the microwire crystallization.