Li-Mg-B-H reactive hydride composite (RHC) has attracted extensive attention over the past decades for its extremely high hydrogen storage capacity (11.5 wt%). But the sluggish desorption kinetics for the second step dehydrogenation reaction need to be further improved. Herein, short rod-like TMTiO3 (TM = Co, Ni) bimetallic oxides, which contain two kinds of transition metal elements, were synthesized and introduced into Li-Mg-B-H RHC for the first time. The NiTiO3 exhibits excellent catalytic effect on the hydrogen desorption kinetic performance of Li-Mg-B-H RHC, and the incubation period for the second step dehydrogenation reaction is eliminated completely by reducing the apparent activation energy for the generation of MgB2 from 296 kJ/mol to 269 kJ/mol. The NiTiO3 doped Li-Mg-B-H RHC can desorb about 9.0 wt% H-2 without obvious attenuation of kinetic performance in five cycles. Mechanism analyses reveal that the in-situ generated nano-sized MgNi3B2 and TiB2 species (similar to 5 nm) both meet the critical value ( < 10%) of the edge-toedge matching model (5.77% for MgNi3B2 and 2.22% for TiB2), which play a significant role in supporting the nucleation of MgB2. Meanwhile, the extremely fine MgNi3B2 and TiB2 heterogeneous nucleation sites can inhibit the excessive growth for a single crystal nucleus of MgB2. The heterogeneous nucleation and grain refinement mechanisms caused by the novel bimetallic oxide could provide alternative insights into designing an in-situ generated nano-sized catalytic hydrogen storage system with enhanced kinetics and cyclic stability for hydrogen-fueled applications. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.