Thiosulfate and p-nitrophenol are two important water pollutants and the presence of them can be harmful for human body. The electro-catalytic interaction between thiosulfate and 2-chloro-N'-[1-(2,5-dihydroxyphenyl)methylidene]aniline, was studied by voltammetric methods. The sensor included carbon paste electrode modified with 2-chloro-N'-[1-(2,5-dihydroxyphenyl) methylidene] aniline and CdO nanoparticle was used as highly sensitive tool for determination of thiosulfate. The proposed sensor resolves overlapping oxidation signals of thiosulfate and p-nitrophenol as two important pollutants for simultaneously determinations. According to the results, it was understood that the proposed working electrode assist to determination of thiosulfate and p-nitrophenol at concentration ranges of 0.09-350.0 and 1.0-550.0 mu M with the respective limits of detection 40.0 nM and 0.5 mu M. The developed working electrode was used for the determination of thiosulfate and p-nitrophenol at different real water samples. (c) 2017 The Electrochemical Society. All rights reserved.