The phase diagram In2Se3-Sb2Se3 was constructed from DTA and X-ray diffraction analysis data. No compound was observed in it, but two finite regions of In2Se3-based solid solutions were found : the first one, called beta＇ (from 10 to 3.5 mol% Sb2Se3), of the tetradymite structure, and the second (from 3.5 to 0 mol% Sb2Se3) being the beta-In2Se3 stabilized form. Crystals of the antimony-doped beta-In2Se3 form were grown by the Bridgman method. This compound, the composition of which is In1.94Sb0.06Se3, appears to be closely connected with the tetradymite structure. The refined unit-cell parameters of the hexagonal cell are a = 397(2) pm and c = 2827(2) pm. Its room temperature de conductivity is 2 x 10(-2) Omega cm(-1), and it is an n-type semiconductor with a band gap of 1.34 eV.