By using anthracene-9-carboxylic acid (9-ACA) as the emitter and palladium(II)-octaethylporphyrin (PdOEP) as the sensitizer, highly effective pH-responsive TTA-UC system was obtained at the optimal mol ratio 80∶1. The UC intensity and pH value showed good linear relationship in the pH range of 4~8 and 8~11, respectively. In the control experiment, fluorescence of 9-ACA did not reveal linear relationship with pH, proving that the broad-range pH responsiveness is derived from the triplet-triplet energy transfer (TTET) process between the sensitizer and emitter.