Abstract: A novel method was developed for directly detection of amino acids in beer by using extractive electrospray ionization mass spectrometry (EESI-MS) without any sample pretreatment. Taking the advantage of multiple-stage tandem MS capability of an ion trap mass analyzer, all the signals detected from beer samples were quickly identified using their characteristic fragments, resulting in confident validation of the analytical results. The average time for a single sample analysis was less than 0.5 min, and the relative standard deviations of the method were in the range of 5.0%-10.0%. The limit of determination of this method was found to be 10^－10 g•mL^－1 for most amino acids.