In the existing study, a new vortex-assisted cloud point extraction (VA-CPE) method was developed for determination of low levels of thiosulfate in environmental waters at 632 nm by spectrophotometry. The method is selectively based on charge-transfer-sensitive ion-pair complex formation of Ag(S2O3)(2) (3-), which is produced by the reaction of thiosulfate with excess Ag+ ions with toluidine blue (3-amino-7-dimethylamino-2-methylphenazathionium chloride, TB+) and then its extraction into micellar phase of polyethylene glycol 4-tert-octylphenyl ether (Triton X-45) in presence of Na2SO4 as salting-out agent at pH 7.0. All the factors affecting complex formation and VA-CPE efficiency were optimized in detail. Under the optimized conditions, the linear calibration curves for thiosulfate were in the range of 0.2-120 and 5-180 A mu g L-1 with sensitivity improvement of 81-folds and 15-folds, respectively, as a result of efficient mass transfer obtained by CPE with and without vortex, while it changed in the range of 260-3600 A mu g L-1 without preconcentration at 642 nm. The limits of detection and quantification of the method for VA-CPE were found to be 0.05 and 0.22 A mu g L-1, respectively. The precision (expressed as the percent relative standard deviation) was in range of 2.5-4.8% (5, 10 and 25 A mu g L-1, n: 5). The method accuracy was validated by comparing the results to those of an independent 5,5'-dithiobis(2-aminobenzoic acid) (DTNB) method as well as recovery studies from spiked samples. It has been observed that the results are statistically in a good agreement with those obtained by DTNB method. Finally, the method developed was successfully applied to the preconcentration and determination of trace thiosulfate from environmental waters.