Tea possesses a large number of healthy properties due to presence of biologically active polyphenolic compounds, first of all, catechins.Using micellar electrokinetic chromatography (MEKC) method it was established that polyphenols have been able to interact with some proteins.These processes explain reduction of biological activity of green and black tea after addition of some milk which contains protein caseine.The rapid decreasing of catechins concentrations is observed when 5 % of milk was added into tea beverages.