A　simple　sensor　utilizing　a　simple　aminoquinoline　derivative　(5-(quinolin-8-yliminol)　pentanal,　QYP)　has　been　successfully　developed　for　the　naked-eye　colorimetric　assay　of　pH.　The　QYP　compound　presents　strong　solvatochromism　due　to　the　solute-solvent　interaction,　and　it　is　sensitive　to　a　pH　change　in　the　solution.　The　color　of　the　solution　changes　from　orange　to　colorless　upon　increasing　the　pH　value,　which　is　well　consistent　with　the　corresponding　UV/vis　absorbance　variation.　UV　absorbance　has　a　direct　linear　relationship　with　the　pH　values　in　the　range　of　4.0　to　8.0　in　phosphate-buffered　saline,　and　the　corresponding　color　variation　could　be　distinguished　readily　by　the　naked　eye.