The present work describes the investigation of electrical and magnetic properties of the glass-coated Co-rich amorphous ferromagnetic microwires, having typical metallic core diameters d = 13–20 μm and tailoring by the direct current Joule heating. During this treatment, a continuous monitoring of the microwire condition was carried out, measuring its resistance by means of a DC bridge circuit. The heating of the microwire sample was provided by a direct current in the range from 20 mA to 63 mA. In this heating currents range, the microwires show a slight change in their resistivity. After annealing the resistivity of microwires may increase of about 1% with respect to as-prepared one. Depends on the heating current, the hysteresis loops of annealed microwires demonstrated the transition from a quasi linear type to a bistable one and vice versa. The maximum of the giant magnetic impedance ratio was observed in such microwires, which had a hysteresis loops describable by a near-zero anisotropy field. •Glass-coated amorphous microwires with composition Co69Fe4Cr4Si12B11 under Joule heating treatment.•Continuous resistivity monitoring of microwires during Joule heating treatment.•Normalized resistivity of annealed microwires may increase in the range of 1%.•Changes of electrical, magnetic and magnetoimpedance properties after annealing.•Microwires having hysteresis loops with a near-zero anisotropy field had a maximum GMI-ratio.