The photoinitiated reaction between vitamin C and xanthone in sodium lauryl sulfate (SDS), hexadecyltrimethylammonium chloride (CTAC), and Triton X-100 micelle solutions at various pH was investigated by time-resolved electron paramagnetic resonance (TR-EPR). The TR-EPR spectra were explained by superimpositions of the xanthone ketyl and the vitamin C radicals, showing that a fast hydrogen abstraction reaction of the excited xanthone from vitamin C progresses around the water-oil interface region of the micelles. The EPR signal intensity of the vitamin C radical showed the notable pH dependence, which seems to be attributable to the acid-base dissociation equilibrium of vitamin C. The results suggested that the present reaction is controlled by the transportation of the excited xanthone and vitamin C to the reaction-progressing region, which is the surface or inside of the micelle, and by the difference of the reactivity between the dissociation forms of vitamin C.