Abstract: The effect of aging microstructure on the fracture behavior of Mg-10Gd-3Y-0.6Zr alloy was investigated.The results show that precipitates in the alloy after low temperature aging at 473 K are finer and denser.Microcracks nucleate at grain boundaries due to grain boundary precipitations (GBPs),and then propagate transgranularly along the preferred orientation.When the aging temperature increases to 523 K,the size of GBPs enlarges.Microvoids nucleate by interface debonding between GBPs and the matrix which is caused by stress concentration at large GBPs;subsequently,their coalescence and growth result in final fracture.Otherwise,smoothing facets on the fracture surface form by microcracks propagating along the interfaces between twins and the matrix,and this tendency is intensified due to the existence of GBPs.When the aging temperature increases,the smoothing facets reduce as the twins and GBPs decrease and the slip deformation intensifies.