Ozonolyses of a series of water-insoluble cyclopent-1-enylbenzenes were carried out both in water and in micellar aqueous solutions composed of sodium 1-dodecyl sulfate (SDS) or polyoxyethylene (10) octylphenyl ether (TX-100). Because the conversion of every substrate in the micellar systems was higher than that in water, the solubilization of substrates by micelles was certainly effective in promoting the ozonolyses of insoluble substrates in an aqueous medium. Ozonolyses of these substrates yielded the corresponding water-participation products, oxoaldehydes, and the corresponding water-nonparticipation products, sec-ozonides, almost exclusively. In water, sec-ozonides were formed predominantly in the ozonolyses of all substrates. The product distribution in micellar systems drastically varied with the combination of substrate and surfactant. The difference in the solubilizing mode of substrates by micelles seems to be the key in determining the product distribution. NMR studies on the location of substrates solubilized in SDS or TX-100 micelles supported this speculation very well.