Abstract: The fatty acid monomer, dimer and polymer and total polymer content in fried soya bean oil and sunflower seed oil were measured to study the changes of these indicators with the duration of frying. The oils examined were either treated experimentally with different methods, namely, frying twisted dough sticks for 12 hr at 240℃, frying twisted dough sticks 2 hr daily for 4 days, frying water-soaked cotton ball for 192 hr at 180℃，or takes from the oils being used for frying dough foods in 12 random restaurants of Changchun City. The results indicated that the polymer content is one of the indicators for determining the severity of deterioration of fried oil.