@@@@Abstract Hydrogen storage materials are the key to hydrogen energy utilisation. In this study, ultrathin K2Ti8O17 nanobelts are fabricated and used to catalyse the hydrogen storage of MgH2. The dehydrogenation temperature of MgH2-5 wt% K2Ti8O17 is 189 °C, rapidly releasing 6.6 wt% H2 in 2.4 min at 280 °C, and 6.0 wt% H2 is instantly absorbed in 33 s at 200 °C. Moreover, the activation energy (Ea) of MgH2-5 wt% K2Ti8O17 decreases to 116.3 kJ mol−1, compared to that of the as-milled MgH2 (177.3 kJ mol−1). In stability test, an excellent capacity retention rate of 88% is obtained even after eight cycles. Compositional and structural analyses demonstrate that stable oxygen vacancies in the K2Ti8O17 (K2Ti8O17-Ov) ultrathin nanobelts are responsible for enhancing the kinetics of the dehydrogenation of MgH2. This strategy provides an avenue for the rational design of catalytic materials for hydrogen storage.