Effect of copper ions on lipid matrix organization of synaptosomal membrane of the marine fish Theragra chalcogramma was investigated. It was demonstrated that interaction of copper ions with these membrane stimulated the process of lipid peroxidation and caused changes in the transbilayer distribution of aminophospholipids. Accessibility of phosphatidylethanolamine was increased more than twice, and of phosphatidylserine more than ten times, that can be explained by changes in asymmetrical structure of lipid matrix of synaptosomal membrane. We suggested, that the main mechanism of copper-stimulated damage in transbilayer organization of the membrane is oxidation of membrane protein sulfhydryl groups.