Abstract: A batch culture technique was used to determine the effects of different doses of Compositae Ordos Wormwood extract （COE） on biohydrogenation of fatty acids,concentration of CLA and trans-11C18：1 in culture medium. The dosage of COE was 0（control）,3,30,300 and 3 000 mg/L mixed culture fluid ,respectively. The sampling time was 2,6 and 24 h, respectively.All COE treatments were tested in triplicate at each sampling time.The results showed that COE treatments tended to reduce C18 polyunsaturated fatty acids biohydrogenation,whereas the concentration of trans-11C18：1 and cis-9,trans-11 CLA in culture medium tended to increase.