TlSr2CuO5 has been synthesized in polycrystalline form. Powder X-ray diffraction studies indicate an orthorhombic structure; space group Pmmm; a = 3.661(2), b = 3.793(1), c = 8.99(3)Å. The presence of short Cu{single bond}O bonds indicates the high formal valence for Cu. TlSr2CuO5 is found to be metallic and no superconductivity could be observed down to 4.2 K. © 1991 Academic Press, Inc.