Sodium borohydride (NaBH4) is considered to be an excellent hydrogen-generation material via hydrolysis. However, it remains challenge to regenerate it after hydrolysis in practical applications. Therefore, a low-cost regeneration method from hydrolysis by-products for recycling is the key issue. In this study, NaBH4 was successfully regenerated by direct high-energy ball milling of magnesium alloy (Mg17Al12) and hydrolysis by-product NaBO2 center dot 2H(2)O with addition of a small amount of NaH. Notably, unlike traditional method, here there is no need of adding extra hydrogen and the H- in the regenerated NaBH4 is mainly from the H+ in the coordinated water. It was found that through adding a small amount of NaH, the highest yield may reach 57% after optimizing the regeneration process. In addition, it is the first time we found that not only Mg can participate in the reaction, but also Al; and the addition of NaH can promote the reaction. Furthermore, the regeneration mechanism of NaBH4 was analyzed and the transition pattern [B(OH)(4)](-)/[BH3(OH)](-)/[BH4](-) was successfully observed during the regeneration process. It is worth emphasizing that NaBH4 can be regenerated through ball milling method, which is energy-saving and suitable for up-scaling in the future. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.