This paper describes a potassium ion-selective electrode based on 2,2-dithiodibenzoic acid with a focus on the sub-Nernstian response characteristics. The topics including the experimental parameters that influence the response of the electrode, useful membrane compositions and applications were investigated. The membrane electrode demonstrate linear (R2= 0.999) sub-Nernstian responses, with the slop of 40.12 ± 0.15 mV/decade, toward potassium(I) ions over the range of 1.0 x 10– 5 to 1.0 M. The prepared electrode, with detection limit of 6.2 x 10-6 M, was successfully applied in the direct potentiometric measurement of sub-milimolar quantities of K+ in aqueous solutions. The results were compared with atomic absorption spectrometry measurements. There was good agreement between the results from the proposed electrode and those from the standard method.