Effects of trace Zr and Er additions on microstructures and mechanical properties of Al-4.4Zn-2.4Mg alloys (mass fraction, similarly hereinafter) were investigated by testing hardness, tensile property, resistivity, and stress corrosion cracking resistance and observing metallographic microstructure of the alloy. The results show that the grain refining effect of Zr addition alone for the alloy is better than that of Er addition alone or Zr-Er co-addition. However the Zr-Er co-addition can obviously inhibit recrystallization behavior of the alloys. The Al-4.4Zn-2.4Mg alloy with Zr-Er co-addition has nearly equal mechanical properties to that with Zr addition alone, while has better stress-corrosion cracking resistance than that with Zr or Er addition alone. The alloys with Zr-Er co-addition possess the optimum combination properties. Zr-Er co-addition can improve the stress-corrosion cracking resistance of the Al-4.4Zn-2.4Mg alloy, which is indirectly realized by the fibrous microstructure obtained from inhibiting recrystallization.