Research subject. Limestones of 11 sections of the Mid-Carboniferous boundary interval in the Southern and Middle Urals were studied. Sections of the western slope of the Urals (2 sections) refer to the East European platform, while the eastern Urals carbonate strata (9 sections) are fragments of the carbonate platform formed in the residual basin of the Ural Ocean. Material and methods. The lithological features of limestones of all considered sections were identified, the distribution and main characteristics of 28 trace (rare and scattered) elements, as well as Al and Fe, were studied and analyzed. Results and conclusions. The main characteristics of sedimentary basins, including the redox state, terrigenous material provenances, climatic conditions and the influence of endogenous processes, primarily volcanism, were clarified and evaluated. The results confirm the point of view about the short-duration hiatus at the Mid-Carboniferous boundary and the absence of a catastrophic drop in the World Ocean level. There are also no evidences of a significant cooling period. Geochemical and lithological data indicate local unconformities, transformations of sedimentary environments and sources of siliciclastic admixtures, as well as some climate humidization at the Mississippian-Pennsylvanian boundary.