alpha-Tl2Te2O5 crystallizes with the monoclinic symmetry (space group P2(1)/n) and unit-cell parameters a = 7.119(1), b = 12.138 (2), c = 8.439 (2) Angstrom, beta = 114.28 (3)degrees, Z = 4. Its crystal structure was solved from single crystal X-ray diffraction data to a final R-1 = 0.0476. The strong stereochemical activity of the lone pairs E of Te and Tl atoms divides the structure into independent Tl2Te2O5 sheets parallel to (10 (1) over bar) and constituted of MO4E trigonal bipyramids sharing edges and corners.