Abstract: Field Desorption Mass Spectrometry (FDMS) is regarded as the method of choice for the analysis of non-volatile and thermally labile substances. At the best anode temperature (BAT)of the field anode, maximum molecular ion current and minimal fragmentation is generated. Bear gall is a famous and precious Chinese drug, no satisfactory identification method was found for the quality control of this drug. We have measured bear, ox, pig, sheep, snake and hen gall using FDMS at BAT to establish a qualiyt control method for bear gall. The spectrum of bear gall differs obviously from the other FD spectra of the mentioned gall. The bear gall adulterated with other animal gall can be identified unequivocally. The FDMS method is simple, reliable and time-saving for the quality control of bear gall.