First principles calculations are performed to study the influence of alloying elements Li, Na, K, Ti, Mn, and Ni and Y vacancy on the stability and dehydrogenation properties of Y(BH4)(3). The formation energies of low and high temperature (LT and HT) phases of alloyed Y(BH4)(3) are evaluated. Ti, Mn, and Ni elements and the Y vacancy containing Y(BH4)(3) systems are endothermic. The Y vacancy is difficult to be generated due to the high energy demand. The alkali metals of Li, Na, and K prefer to occupy the interstitial sites in both the LT and HT phases of Y(BH4)(3), especially the K element. The K containing systems show negative formation energy, even if eight K atoms are introduced. The K containing systems show similar structure characteristics with the KY(BH4)(4) compound. Therefore, a phase transition from the K alloyed Y(BH4)(3) to KY(BH4)(4) is expectable. However, the transition from Li/Na alloyed Y(BH4)(3) to corresponding Li/Na Y(BH4)(4) compounds is energetically unfavorable. Electronic structures of alloyed Y(BH4)(3) are investigated to explore the reasons that why only K alloyed Y(BH4)(3) can transform to KY(BH4)(4) compound. In term of dehydrogenation properties, all alloyed systems show smaller dehydrogenation energies than the pure Y(BH4)(3). The concentrations of alloying elements can greatly affect the dehydrogenation properties of alloyed Y(BH4)(3). Copyright (c) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.