The Tl2Se-In2Se3 cross section of the Tl-In-Se system was studied by both the common thermal analysis (TA) and the X-ray diffraction (XRD). From the results of the studies the phase diagram for the quasi-binary Tl2Se-In2Se3 system was delineated for the first time. Numerical values of the phase transition temperatures at different alloy compositions within the whole concentration range have been listed in a table. The existence of two ternary compounds TlInSe2 and TlIn5Se8 was established. (C) 2012 Elsevier B.V. All rights reserved.