Nanometric-sized isolated inclusions have been studied in six cloudy octahedral diamonds from Internationalnaya and Yubileynaya mines (Yakutia). Transmission electron microscopy (TEM) techniques such as electron diffraction, AEM, EELS and HREM were applied. All crystals exhibit octahedral external habit with cloudy cores which contain numerous micro- and nanoinclusions, each of them is composed of multi-phase assemblages, which include solid phases (silicates, oxides, carbonates), brines (halides) and fluid bubbles. All inclusions are relatively homogenous in composition and contain the distinguishable crystalline and fluid phases. Al-bearing high–Mg silicate, Ca,Mg-carbonates, Ba-carbonate, Sr-carbonate, phlogopite, ilmenite, apatite, magnetite, K,Fe-sulfides and kyanite have been identified as crystalline mineral phases by electron diffraction patterns, except of Ba and Sr-carbonate. Halide phase is KCl. Bubbles contained high K, Cl, O, F, P and less S, Ba, Si, Ti components. Carbonates were identified in TEM foils from all studied diamonds in all assemblages with silicates, oxides, sulfides. Some elemental variations may be explained by fractional crystallization of such fluid/melt or mixing of fluids with different compositions (carbonatitic, hydrous-silicic, brines).