The results suggested that the repeated plastic deformation (RPW) process prior to hot extrusion has a great effect on improving ageing response of the as-extruded Mg–6Zn–1Er alloy. The rod-like β1′ phase was promoted to precipitate abundantly during isothermal ageing treatment, which mostly contributed to the highest peak hardness of 98.6 (±2.0)HV in the alloy treated by 300 repeated plastic working circles. Furthermore, the peak-aged alloy displayed the highest tensile strength, and the values of the ultimate tensile strength and yield tensile strength were about 360MPa and 252MPa, respectively.