Abstract: Morphine-3-β-D-glucuronide, morphine, codeine and O⁶-monoacetylmorphine in heroin addicts’ urine samples were analyzed by liquid chromatography-tandem mass spectrum(LC-MS/MS). The urine samples were extracted by solid phase extraction(SPE), isolated by the C₁₈ column and then analyzed by MS. The positive electric spray ionization mode was applied, multiple reaction monitoring(MRM) mode was used to analyze target compounds. Identification was based on retention time and two pairs of precursor-to-product ion transitions. The limit of detection(LOD) is 0.1 μg•L^-1 for morphine, codeine, O⁶-monoacetylmorphine and 0.5 μg•L^-1 for morphine-3-β-D-glucuronide, the relative standard deviation of intra and inter day precision are less than 10%. The method shows high sensitivity and selectivity, and is suitable for the analysis of morphine-3-β-D-glucuronide, morphine, codeine, O⁶-monoacetylmorphine in heroin addicts’ urine samples.