Abstract: A HPLC-MS/MS method for detection of biurea (HDC) which was the metabolite of flour additive azodicarbonamide during processing in flour was established.HDC was extracted by pure water, purified on a LC-18 solid phase extraction cartridge, and then determined by HPLC-MS/MS.ESI in positive ion mode was used as the ionization source.Selected ions were monitored by multiple reaction monitoring (MRM) .It was separated by an amido column and the acetonitrile and water (volume ratio was 70:30) was used as mobile phase.The monitor ion pairs (m/z) were 119/76 and 119/59.The limit of detection was 0.1μg/kg, the rate of recovery ranged from 89.00%to 102.73%with relative standard deviation≤5.0% (n=5) .