Abstract The giant stress-impedance (GSI) effect in as-cast and DC current annealed Co 71.8Fe 4.9Nb 0.8Si 7.5B 15 amorphous glass-covered wires is presented. The SI ratio of the as-cast sample exhibits negative GSI effect. For the sample annealed by 60 mA DC current, the SI ratio first increases with applied tensile stress, then decreases. The maximum Δ Z/Z ratio of 304% is obtained. Frequency dependence in the range from 1 to 110 MHz of the GSI effect is investigated. Experimental results show that the real part R and the imaginary part X of impedance play an important role at high frequency and low frequency, respectively. At 1 MHz, the maximum Δ X/X ratio of 1 448% is obtained. At 110 MHz, the maximum Δ R/R ratio of 648% is obtained.