Objective:To determine the related substances in dexibuprofen and its sustained release tablets by HPLC .Methods:The related substances including a-methyl-4-butyl benzene acetic acid , L-ibuprofen and the others were detected by HPLC .An Agilent Eclipse XDB-C18 column (150 mm ×4.6 mm, 5 μm) was used for a-methyl-4-butyl benzene acetic acid and the other related sub-stances.A Kromasil 5-TBB column (250 mm ×4.6 mm, 5 μm) was used for L-ibuprofen.The mobile phases was acetonitrile and phosphate solution (45 ∶55, pH value was adjusted to 2.5 by phosphoric acid), hexane-tert-butyl ether-acetic acid (850 ∶150 ∶1), acetonitrile and sodium acetate buffer (60 ∶40, 6.13g sodium acetate was dissolved in 750ml water, and pH was adjusted to 2.5 by glacial acetic acid ) , respectively .The detection wavelength was 214 nm, 220 nm and 263 nm, respectively .The flow rate for a-meth-yl-4-butyl benzene acetic acid and the other related substances was 1.0 ml· min-1 .The flow rate for L-ibuprofen was 2.0 ml· min-1 . The column temperature was 30℃and the injection volume was 20 μl.Results:The method could effectively detect the contents of a-methyl-4-butyl-phenylacetic acid and L-ibuprofen, and identify and separate the related substances in dexibuprofen raw material and its sustained release tablets .Conclusion:The method is specific , accurate and easy to operate , which can be used for the quality control of ibuprofen raw material and its sustained release tablets .