With a view to guide-antioxidant activity for oil, two compounds were isolated from Vitex negundo L. seeds by polyamide and silica gel chromatographic methods, and identified to be isofraxidin(I) and 6 - hydroxy - 4 - (4 - hydroxy - 3 - methoxyphenyl) - 3 - hydroxymethyl - 7 - methoxy - 3, 4 - dihydro - 2 - naphthaldehyde(II) respectively by spectroscopic method. The antioxidant effect of both w(I)=0.04% and w(II)=0.06% was better than that of w(BHT)=0.02% in lard, and the effect increased with increasing concentration.