The purpose of this study was to explain how extracts from chokeberry and blackcurrant interact with the lipid phase of biological membrane and with human albumin - the main protein of blood. Aiming at better understanding of the observed biological activity of the extracts, we also conducted experiments with their main components: cyanidin-3-0-galactoside and cyanidin-3-0-ruthinoside. Antioxidant activities of extracts and cyanidin derivatives were investigated with phosphatidy1choline liposomes and AAPH as oxidation inducing factor. Fluorescent probes (merocyanin and N-phenyl-1-naphthylamine) that were located at different depths within the membrane lipid bilayer were also used. The interaction between the compounds and human serum albumin was investigated using natural fluorescence quenching. According to our study it is highly likely that the significant antioxidant activity of chokeberry and blackcurrant extracts (IC₅₀chokeberry = 4.92 pg/mL; IC₅₀blackbcurrant = 7.04 μg/mL) is probably due to cyjanidin's main derivatives, which protect the lipid membrane more than the extracts. In addition, it has been suggested that the compounds are anchored mainly on the membrane surface and rigidify/order the lipids in the membrane. That rigidifying effect is the key factor for understanding their antioxidant properties. Experimental results have proved that all the study compounds quench the fluorescence of HSA through a static mechanism and the main interaction forces are the Van der Waals and hydrogen bonding interactions. The results of the study have improved our knowledge on how to protect membranes against lipid peroxidation using extracts rich in anthocyanins. The results can be relevant to pharmacists and nutritionists.