Precise determination of pH values of strong basic solution is appealing and challenging. Herein, a voltammetric method for measuring pH of strong basic solution was developed using Ag3PO4 shell@Ag core nanoparticles as a pH indicator. Ag nanoparticles (AgNPs) were electrodeposited on Au electrode surface and then were electrochemically oxidized to form Ag+. A layer of Ag3PO4 was in‐situ formed on the surface of AgNPs by precipitation with PO43− in solution. As an electroactive species, Ag3PO4 can undertake an electrochemical redox reaction and its reduction peak potential is linear with pH values of solution in the range of 10–14. The slope of the linear equation is about −0.0196, which is consistent with that calculated by the Nernst equation. The resultant AgNPs/Ag3PO4 modified electrode has been successfully applied in the determination of pH of strong basic solution. The proposed voltammetic method for measuring pH value overcomes the shortcoming of pH glass electrode under strong basic environments.