Phase stability and thermal expansion of rock-salt Me1-xZnxO (Me = Ni2+, Co2+, Fe2+, Mn2+) solid solutions synthesized at high pressures and high temperatures have been studied by synchrotron X ray diffraction in a wide (0.1 ≤ x ≤ 0.8) concentration range. At ambient pressure rs-Me1-xZnxO solid solutions were found kinetically stable up to 670-1100 K depending on the composition and type of Me2+ cation. Temperature-induced decomposition of the single-phase rock-salt solid solutions lead in most cases to the formation of a mixture of two solid solutions, with cubic and wurtzite structures. Oxidation of the Me2+ cation (Co, Mn) by atmospheric oxygen can result in formation of mixed higher oxides of these metals. In all the systems studied, the rock-salt solid solutions show a linear temperature dependence of the thermal expansion, but for the compositions with the highest ZnO content, deviations from the linear dependence are observed.