The effect of terephthalic acid, which is found in foodstuffs as a monomer of fat-soluble vitamins such as vitamin A, D3 and alpha-tocopherol was examined in model tests of terephthalic acids, and of foils composed of polyterephthalic acid esters. Vitamin A and D3 were stabilized by terephthalic acid (the vitamin content was up to 25% after adding terephthalic acid, depending on temperature and duration of heating); alpha-tocopherol was reduced a little faster with terephthalic acid. Heated in the foil the vitamin content was not reduced as much as in the model tests with terephthalic acid.