The paper describes a method for the recovery of Cs-137 from an aqueous radioactive laboratory waste solution containing Cs-137 (2 mu g/mL) in the presence of high concentration of Na+ using solvent extraction technique. The method comprises of adjustment of pH to the acidic range (pH = 2), contacting the aqueous radioactive solution with sodium tetraphenylboron (TPB) in nitrobenzene, whereby Cs-137 binds with tetraphenylboron anions and gets separated. Results of this investigation indicate that Cs-137 could be efficiently and selectively extracted from an aqueous solution media containing high concentration of Na+ under mildly acidic pH into an organic phase and back extracted with small volume of 3M HNO3, thus enabling concentration. The proposed method was successfully applied in real samples.