Based on the ab initio calculations, we propose a new class of three dimensional (3D) topological insulators in alkali-metals-based ternary intermetallic compounds X 2 YZ (X=alkali metals, Y=Ag, Z=Sb) with a highly ideal assumption that the X 2 YZ compounds would crystallize in a cubic lattice. The band topology of X 2 YZ is explored by using full-potential linear augmented plane wave method. The results reveal that the topological insulator state of X 2 YZ can be realized by applying a uniaxial tensile strain of greater than 3% along the [001] direction and the electronic structure exhibits a distinct band-inversion feature. This new X 2 YZ compounds provide an alternate platform for novel quantum phenomena and multifunctional topological devices.