Abstract: To investigate the antioxidant effects of 4 antioxidants on oil under UV light. The effect of acid value,peroxide,malondialdehyde-value,conjugated diene and conjugated trienes compounds in lard by using butylated hydroxyanisole(BHA),2,6-Di-tert-butyl-4-methylphenol(BHT),tert-Butylhydroquinone(TBHQ)and Propyl gallate(PG)under 254,365 nm were studied. The results showed that,compared with the blank test sample,the differences of acid value,peroxide,malondialdehyde-value,conjugated diene and conjugated trienes compounds at 254 nm light between BHA,BHT,PG were not significant(p>0.05).The differences of acid value,peroxide,conjugated diene and conjugated trienes compounds at 365 nm light between 4 antioxidants and blank test sample were not significant(p>0.05),difference of malondialdehyde value was extremely significant(p<0.01).As for acid value,the differences of conjugated diene and conjugated trienes compounds between TBHQ and blank test sample were not significant(p>0.05),the peroxide and conjugated trienes were significant(p<0.05),difference of malondialdehyde value was extremely significant(p<0.01). It was concluded that BHA,BHT and PG had no antioxidant effect under 254,365 nm UV Light irradiation,and TBHQ was also not ideal.