Novel fluorometric receptor (R) designed base on amino-thiadiazole calix[4]arene. R displayed selective fluorescence shift for Ag+ ion among 20 different metal ions. R-Ag exhibited enormous Ka with stoichiometry of 1:1. DFT computational calculations modeled the electrostatic charges of heteroatoms. Competitive tests exhibited the excellent specificity of R toward Ag+. High recognition efficiency in physiological medium was observed.