Hydrogen storage materials with a low working temperature are strongly required for the application of the next generation on-board hydrogen storage system. Among several hydrogen storage materials, complex borohydrides are thought to be a promising candidate, if their desorption temperature is decreased down to ambient temperature. For such purpose, it is very important to understand the mechanism behind the hydrogen desorption reaction. Particularly, we have found the importance of hydrogen diffusion in solids in order to accelerate the hydrogen desorption reaction, based on our muSR measurements on MgH2. We believe that this is a common parameter to determine the desorption temperature for other hydrides. In order to confirm this, we would like to study a diffusive behavior for several complex borohydrides until their hydrogen desorption temperature with muSR.