A method was developed for the determination of AHLs （N-Hexanoyl-DL-homoserine lactone（C6-HSL） and N-Octanoyl-DL-homoserine lactone（C8-HSL） were chosen as the representatives) in activated sludge in MBRs by solid phase extraction（SPE） combined with ultrahigh pressure liquid chromatography-tandem mass spectrometry（UHPLC-MS/MS）. The results showed that C6-HSL and C8-HSL presented good linear relations（R2＞0.998） in the range of 1~200 μg/L. The limit of detection and quantitation were 0.100 μg/L and 1.000 μg/L, respectively. The average recoveries of AHLs at three spiked concentrations were in the range of 80.69%~83.75%, and the relative standard deviations（RSD） were 4.71%~7.25%. The developed method is sensitive, stable and has weak matrix effects, which is applicable to determine the trace AHLs in activated sludge in MBRs.