Herein,　gold-silver　bimetallic　nanoclusters　(Au-Ag　NCs)　with　the　high　fluorescent　intensity　were　first　synthesized　successfully　and　utilized　for　the　fabrication　of　sensitive　and　specific　sensing　probes　toward　inorganic　pyrophosphatase　(PPase)　activity　with　the　help　of　copper　ion　(Cu2+)　and　inorganic　pyrophosphate　ion　(PPi).　Cu2+　was　used　as　the　quencher　of　fluorescent　Au-Ag　NC,　while　PPi　was　employed　as　the　hydrolytic　substrate　of　PPase.　The　system　consisted　of　PPi,　Cu2+　ion,　and　bovine　serum　albumin　(BSA)-stabilized　Au-Ag　NC.　The　detection　was　carried　out　by　enzyme-induced　hydrolysis　of　PPi　to　liberate　copper　ion　from　the　Cu2+-PPi　complex.　In　the　absence　of　target　PPase,　free　copper　ions　were　initially　chelated　with　inorganic　pyrophosphate　ions　to　form　the　Cu2+-PPi　complexes　via　the　coordination　chemistry,　thus　preserving　the　natural　fluorescent　intensity　of　the　Au-Ag　NCs.　Upon　addition　of　target　PPase　into　the　detection　system,　the　analyte　hydrolyzed　PPi　into　phosphate　ions　and　released　Cu2+　ion　from　the　Cu2+-PPi　complex.　The　dissociated　copper　ions　readily　quenched　the　fluorescent　signal　of　Au-Ag　NCs,　thereby　resulting　in　the　decrease　of　fluorescent　intensity.　Under　optimal　conditions,　the　detectable　fluorescent　intensity　of　the　as-prepared　Au-Ag　NCs　was　linearly　dependent　on　the　activity　of　PPase　within　a　dynamic　linear　range　of　0.1-30　mU/mL　and　allowed　the　detection　at　a　concentration　as　low　as　0.03　mU/mL　at　the　3sblank　criterion.　Good　reproducibility　(CV　©　2016　American　Chemical　Society.