A printed flexible PH sensor is provided. The printed flexible PH sensor includes a flexible substrate. A working electrode is disposed on the flexible substrate, and the working electrode includes a first silver layer formed on the flexible substrate by an ink-jet printing process, a second silver layer formed on the first silver layer by a silver mirror reaction, and a metal oxide layer disposed on the second silver layer of an end portion of the working electrode. A reference electrode is disposed on the flexible substrate, and the reference electrode includes the first silver layer and the second silver layer formed on the first silver layer, and a silver chloride layer totally covering the second silver layer. A method for fabricating the printed flexible PH sensor is also provided.