In this work, the complex hydrogen sorption behaviors in a 3NaBH(4)/HoF3 composite prepared through mechanical milling were carefully investigated, including the reactions occurred during ball milling and de-/rehydrogenation processes. Different from other rear earth fluorides, the HoF3 can react with NaBH4 during ball milling, leading to the formations of Na-Ho-F and Na-Ho-BH4 complex compounds. The first dehydriding of the 3NaBH(4)/HoF3 composite can be divided into 4 steps, including the ion exchange between H- and F-, the formation of NaHo(BH4)(4), the decomposition of NaHo(BH4)(4) and reaction of NaBH4 with Na-Ho-F compounds. The final products, HoB4, HoH3 and NaF, can be rehydrogenated to generate NaBH4 and NaHoF4 with an absorption capacity of 2.3 wt% obtained at 400 degrees C. Based on the Pressure-Composition-Temperature measurements, the de-/rehydrogenation enthalpies of the 3NaBH(4)/HoF3 composite are determined to be 88.3 kJ mol(-1) H-2 and -27.1 kJ mol(-1) H-2, respectively. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.