The influence of the nature of phase-transfer catalysts on the efficiency of extraction of W(VI) and P(V) peroxyheteropoly compounds to the organic phase during epoxidation of olefins under the phase-transfer catalysis (PTC) conditions was studied. It was found that the efficiency of phase transfer depends on the size of alkyl radicals and availability of the charge of the PTC cation. It was shown that, in order to enhance the extraction, it is necessary to maintain the stoichiometric ratio between W and P in accordance with the composition of prevalent complexes. An excess of a phase-transfer agent was found to decrease the selectivity for epoxide.