Co-substituted NiZn ferrite thin films, Ni0.5Zn0.5CoxFe2−xO4 (0≤x≤0.2), were synthesized by the sol–gel process. The structure and magnetic properties of Ni0.5Zn0.5CoxFe2−xO4 ferrite thin films have been investigated. The diffraction peak shifted towards the lower angle and the lattice parameter increased with Co substitution. There is little influence of Co substitution on the microstructure of NiZn ferrite thin films. The saturation magnetization gradually increases with the increase in Co substitution when x≤0.10, and decreases when x>0.10. Meanwhile, the coercivity initially decreases with the increase in Co substitution when x≤0.10, and increases when x>0.10. ► The diffraction peak shifts towards the lower angle and the lattice parameter increases with Co substitution. ► There is little influence of Co substitution on the microstructure of NiZn ferrite thin films. ► Proper concentration of Co substitution can improve the magnetic properties of NiZn ferrite thin films.