The effects of Co addition on the microstructure,crystallization processes and soft magnetic properties of(Fe1 xCox)83Si4B8P4Cu1(x?0.35,0.5,0.65)alloys were investigated.The experimental results demonstrated that the addition of Co decreased the thermal stability against crystallization of the amorphous phase,and thus improved the heat treatment temperature of this alloy.Fe Co Si BPCu nanocrystalline alloys with a dispersedα0-Fe Co phase were obtained by appropriately annealing the as-quenched ribbons at 763 K for 10 min.Theα0-Fe Co with grains size ranging from 9 to 28 nm was identified in primary crystallization.The coercivity(Hc)markedly increased with increasing x and exhibited a minimum value at x0.35,while the saturation magnetic flux density(Bs)shows a slight decrease.The(Fe0.65Co0.35)83Si4B8P4Cu1nanocrystalline alloy exhibited a high saturation magnetic flux density Bsof 1.68 T,a low coercivity,Hcof 5.4 A/m and a high effective permeability meof 29,000 at 1 k Hz. The effects of Co addition on the microstructure, crystallization processes and soft magnetic properties of (Fe1 xCox) 83Si4B8P4Cu1 (x? 0.35,0.5,0.65) alloys were investigated. The experimental results of that the addition of Co decreased the thermal stability against crystallization of the amorphous phase, and thus improved the heat treatment temperature of this alloy. Fe Co Si BPCu nanocrystalline alloys with dispersed α0-Fe Co phase were obtained by annealing the as-quenched ribbons at 763 K for 10 min. grains size ranging from 9 to 28 nm was identified in primary crystallization. The coercivity (Hc) markedly increased with increasing x and extracted a minimum value at x 0.35, while the saturation magnetic flux density (Bs) shows a slight decrease. ( Fe0.65Co0.35) 83Si4B8P4Cu1nanocrystalline alloy exhibited a high saturation magnetic flux density Bsof 1.68 T, a low coercivity, Hcof 5.4 A / m and a high effective permeability meof 29,000 at 1 k Hz.