Abstract: UHPLC-MS/MS was applied to the detection of morphine-3-glucuronide in blood and urine. The blood or urine sample (1.00 mL) was extracted with 3 mL of the mixture of acetonitrile and methanol (6+1). After centrifugation, the supernatant was evaporated to near dryness by N₂-blowing at 40℃ in the water bath. The residue was taken up with 0.2 mL of methanol. The solution was filtered on 0.22 μm microporous filtering film.Boston ODS chromatographic column was used as stationary phase, and the mixture of 0.1% (φ) formic acid solution and methanol mixed in different ratios was used as mobile phase in gradient elution. ESI⁺, MRM and EPI were adopted in MS/MS. Retention time and characteristic ion pair were used to identify the sample. Detection limit (3S/N) of the method was 5 μg·L^-1.