The lattice parameters, bulk modulus, first derivative of the bulk modulus, electronic band structures, phonon dispersion curves and phonon density of states calculations for Li2AlGa and Li2AlIn Heusler alloys are performed and compared in this study using density functional theory within the generalized gradient approximation. Computed lattice parameters display a good agreement with the literature. Obtained electronic band structures of both Heusler alloys show that they are in semi-metallic structure. Phonon dispersion curves and the phonon density of states graphs are also obtained in order to study the lattice dynamics of these Heusler alloys. It is noticed that Li2AlGa and Li2AlIn Heusler alloys are dynamically stable in the ground state.