Extraction separation and concentration of Cs and Sr from aqueous solutions, containing macroconcentrations of competitive ions (Li + , Na + , K + , Mg 2 + , Ca 2 + , Al 3 + , Fe 3 + ) by the nitrobenzene solutions of bis-1,2-dicarbollylcobaltate in the presence of linear and cyclic polyoxonium compounds (POC) has been investigated. It has been found, that the addition of DB18C6 increases the distribution ratio of cesium (D C s ) but the addition of other crowns and PEG decreases D C s value and selectivity of D S r and the selectivity of Sr/Ca separation. Separation factors of Sr/Ca increase from α(Sr/Ca) 2 (found in the absence of POD) to α(Sr/Ca) 50 (for DB18C6), α(Sr/Ca) 100 (for 18C6 and DCH18C6) and α(Sr/Ca) 1000 for 15C5.