Effect of aging treatment on the microstructure, creep resistance, and high temperature mechanical properties of the Mg-6Zn-3Cu alloy (ZC63) with La- and Ce-rich rare earth additions was investigated by impression creep and shear punch tests (SPT). Impression creep tests were performed in the temperature range 423-498 K and under punching stress in the range 150-700 MPa for dwell times up to 3600 s. The ultimate shear strength (USS) was measured by the SPT in the temperature range 298-498 K. The results showed that aging treatment increased the shear strength of the cast alloys, whereas it had detrimental effects on the creep strength of materials. These observations were discussed on the basis of the microstructural features and phase constituents of the investigated alloys in the as-cast and aged conditions. (C) 2014 Elsevier B.V. All rights reserved.