The dimerization of bile salts is known to be the critical step in the formation of bile salt micelles. The influence of a sodium cholate dimer, synthesized by linking two cholic acid molecules via spacer, on the micellization processes of selected bile salts has been investigated. Fluorescence studies of a pyrene probe and NMR spin-lattice relaxation time experiments have been carried out to determine the critical micellar concentration (cmc) of sodium cholate and sodium glycocholate upon the addition of various amounts of the dimer. The cmc＇s of the bile salts are significantly lowered by the presence of this dimer, which indicates that the sodium cholate dimer can facilitate the micellization of bile salts.