Carbon and oxygen isotope compositions have been determined for carbonate minerals from different types of carbonatites (large carbonatite bodies, veins, eruptive breccia), as well as from different temperature classes of carbonatites (according to Samoilov [1]). It could be shown, that only high temperature carbonatites exhibit small variations of δ18O and δ13C falling in the range of “high temperature mantle carbonates”, whereas low temperature calcites and dolomites show wide variations in δ18O. These changes in both isotope and mineral compositions of low temperature carbonatites are interpreted as a result of repeated interaction with fluids. The oxygen isotope ratios in most of the eruptive breccia have been changed by secondary processes. The primary deep-seated isotope record has been preserved only in samples, in which carbonate occurs as fine-grained calcite groundmass.