The interaction between novel asymmetrical porphyrin 5,10,15-triphenyl-20-pyridyl porphyrin and ascorbic acid has been studied by fluorophotometry. It has been found experimentally that in the presence of CTMAB micro-emulsion, the absorption and fluorescence intensity of the porphyrin was greatly enhanced. The addition of ascorbic acid caused the decrease of the intensity, and there was a linear relationship between the fluorescence quenching value and the concentration of ascorbic acid in certain extent. Based on this phenomenon, a new fluorescence quenching method for the determination of ascorbic acid was established, and utilized in the determination of commercial tablets with satisfactory results. The quenching mechanism between porphyrin and ascorbic acid was preliminary studied, and the quenching was belonging to static quenching.