We present a detailed study of the kinetics of photodimerization of 12-(9-anthroyloxy)stearic acid, 12-AS, in cetyltrimethylammonium chloride and polyoxyethylene(10) lauryl ether micelles. The primary objective of this study is to analyze the consequences of the distribution of reactant by the micelles on the reaction kinetics. It was found that the influence of stochastic effects on the photodimerization cannot, by itself, account for the deviation from a homogeneous media kinetics, and interchange of 12-AS molecules between micelles has to be invoked to explain the experimental data. Further, besides the stable head-to-tail dimer a non-negligible amount of a thermally unstable head-to-head photodimer is observed. It is concluded that the inhibition of photochemical bimolecular reactions, such as photodimerization, in compartmentalized media results from two factors : shortness of reactants within the mean displacement distance of the excited species and, in a more pronounced manner, the depletion of available reactants as reaction proceeds in the non-homogeneous media.