A new calix[4]arene containing benzothiazolyl pendants was synthesized and used as an ionophore to fabricate macro- and micro-Ag⁺ selective membrane electrodes. PVC membranes plasticized with NPOE provided better selectivity coefficient towards Ag⁺ than those plasticized with DOS. The selectivity coefficients (log K_{Ag, j}^pot) for macro- and microelectrode were, respectively, -2.8 and -2.5 for Hg(II) and lower than -4.0 and -3.5 for other cations tested. The fabricated electrodes can be used in a wide pH range (pH 2-8) with a response time less than 5 s. The electrodes exhibit near theoretical Nernstian slope (59.7 ± 0.8 mV decade^-1 for macroelectrode and 59.8 ± 1.0 mV decade^-1 for microelectrode) with low detection limits (ca. 5.0 × 10^-7 M) and wide linear working range (10^-6 to 10^-2 M). The electrodes were used as an indicator electrode for the argentometric titration of the mixture of Cl^- and Br^-. The fabricated electrodes were also used for the first time in speciation analysis of Ag nanoparticles with good accuracy and precision. This Ag-ISE should be beneficial to researches regarding Ag nanoparticles.