A new process for selective separation of cesium from acidic nuclear waste solution has been described using 1,3-dioctyloxycalix[4]arene-crown-6 (CC6)/n-dodecane modified with isodecyl alcohol. The process solvent was optimized as 0.03 M CC6 + 30% isodecyl alcohol/n-dodecane for efficient recovery of cesium. The solvent has shown strong extraction ability for cesium between 1 and 6.0 M nitric acid. Stoichiometry of the extracted complex determined by slope analysis method reveals 1:1:1 molar ratio for Cs+, CC6 and HNO3. Extraction of cesium was found to be independent of nitrate ion concentration, possibly due to formation of solvated free ions CsCC6(+)center dot HNO3 and NO3- in the organic medium. Extracted cesium from organic phase was readily stripped with deionized water. Radiolysis of the process solvent up to an absorbed dose of 0.6 MGy produces essentially no deterioration in its performance. Countercurrent mixer-settler experiments with four extraction, two scrubbing and four stripping stages gave about 99% recovery of cesium with very high selectivity from simulated high level waste solution. The results demonstrated the effective use of CC6 + isodecyl alcohol/n-dodecane for separation of cesium from acidic high level waste solution. (C) 2014 Elsevier B.V. All rights reserved.