Previous work on the binary phase diagram (CsNO3 + TlNO3) showed, in particular, the existence of a continuous solid solution, CsxTl1-xNO3. It extends over the whole composition range between T = 430 K and T = 480 K. Mixing enthalpies of the solid solutions CsxTl1-xNO3 are measured at T = (473 +/- 1) K, for the first time, by using a drop calorimetric method. They exhibit a positive and asymmetrical deviation from ideality. (C) 2015 Elsevier Ltd. All rights reserved.