Graphene nanosheets (GNSs) reinforced aluminum-magnesium (Al-Mg) matrix composite foams (G-AMCFs) were successfully prepared by ball milling and powder metallurgy foaming. The effects of GNSs on pore morphology, microstructure and quasi-static compressive mechanical properties of Al-Mg foams were studied. The results show that the addition of GNSs can increase pore nucleation sites and cause the segregation of magnesium oxide (MgO) around the GNSs. With the increment of GNSs content, the pore size of G-AMCFs increases. The compressive mechanical properties of 0.25 wt% G-AMCFs are the best. Compared with Al-Mg foams, the energy absorption capacity, yield strength and plateau stress of 0.25 wt% G-AMCFs are increased by 43.6%, 42.9% and 28.1%, respectively. Meanwhile, 0.25 wt% G-AMCFs show good ductile deformation behavior. The cell structure with high content of G-AMCFs (0.75 wt%) deteriorates which leads to a decrease in mechanical properties, but the yield strength is still higher than that of Al-Mg foams. The enhancement mechanism of compo-site foams includes dispersion strengthening, load transfer and precipitation strengthening.