Y(BH4)(3) is one of the candidates for solid-state hydrogen storage, which contains 9.06 wt% of hydrogen. In this study, the thermal properties of Y(BH4)(3) synthesized via two different methods are extensively examined. One method relies on the solid-solid metathesis reaction between LiBH4 and YCl3, and the other method is the gas-solid reaction between B2H6 and YH3. The two samples are studied by differential scanning calorimetry, thermogravimetry, and X-ray diffraction. They exhibit distinctly different polymorphic phase transformation and melting. It turns out that the side product LiCl in the metathesis reaction, which has been regarded as being inert, shifts the melting point and promotes the formation of YB4 during decomposition. Differential scanning calorimetry and in situ X-ray diffraction data indicate that the addition of LiBH4 to Y(BH4)(3) induces co-melting as is found in the cases of LiBH4-Ca(BH4)(2) or LiBH4-Mg(BH4)(2). Melt infiltration of Y(BH4)(3) into mesoporous carbon cage confirms such melting behavior. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.