A transition metal-containing Zintl phase, Sr2MnSb2, was prepared from a stoichiometric combination reaction of the elements in Sn flux, and its structure was determined by single-crystal X-ray diffraction methods. The compound crystallizes in the orthorhombic space group Pnma with a = 15.936(3) angstrom, b = 14.498(3) angstrom, c = 8.2646(17) angstrom, and Z = 12. The structure of Sr2MnSb2 is composed of corrugated layers of comer- and edge-shared MnSb4 tetrahedra. The basic building unit of the layer is a [Mn3Sb6](12-) cluster composed of three edge-shared MnSb4 tetrahedra. These trinuclear clusters share four Sb vertexes to form a layer with cavities. Sr2+ cations are located at the inter-and intralayer space. Magnetic susceptibility measurements indicate an effective magnetic moment of 4.85 mu(B), a value smaller than what would be expected from Mn2+ ions.