To improve the hydrogen storage properties of Mg-based alloys, a composite material of MgH_2 + 10wt%LaH_3 + 10wt%NbH was prepared by a mechanical milling method. The composite exhibited favorable hydrogen desorption properties, releasing 0.67wt% H2 within 20 min at 548 K, which was ascribed to the co-catalytic effect of LaH_3 and NbH upon dehydriding of MgH_2. By contrast, pure MgH_2, an MgH_2 + 20wt%LaH_3 composite, and an MgH_2 + 20wt%NbH composite only released 0.1wt%, 0.28wt%, and 0.57wt% H2, respectively, under the same conditions. Analyses by X-ray diffraction and scanning electron microscopy showed that the composite particle size was small. Energy-dispersive X-ray spectroscopic mapping demonstrated that La and Nb were distributed homogeneously in the matrix. Differential thermal analysis revealed that the dehydriding peak temperature of the MgH_2 + 10wt%LaH_3 + 10wt%NbH composite was 595.03 K, which was 94.26 K lower than that of pure MgH_2. The introduction of LaH_3 and NbH was beneficial to the hydrogen storage performance of MgH_2. To improve the hydrogen storage properties of Mg-based alloys, a composite material of MgH_2 + 10 wt% LaH_3 + 10 wt% NbH was prepared by a mechanical milling method. The composite exhibits favorable hydrogen desorption properties, releasing 0.67 wt% H2 within 20 min at By contrast, pure MgH_2, an MgH_2 + 20wt% LaH_3 composite, and an MgH_2 + 20wt% NbH composite only released 0.1wt%, 0.28wt% wt%, and 0.57 wt% H2, respectively, under the same conditions. Analyzes by X-ray diffraction and scanning electron microscopy showed that the composite particle size was small. Energy-dispersive X-ray spectroscopic mapping called that La and Nb were distributed homogeneously in the matrix. Differential thermal analysis revealed that the dehydriding peak temperature of the MgH_2 + 10 wt% LaH_3 + 10 wt% NbH composite was 595.03 K, which was 94.26 K lower than that of pure MgH_2. The introduction of LaH_3 and NbH wa s beneficial to the hydrogen storage performance of MgH_2.