Abstract: A method of ultra performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS) was developed for the simultaneous determination of four opium poppy husk alkaloids (i. e., cocaine, codeine, morphine and papaverine hydrochloride) in the residues of foods. The samples were extracted by methanol (containing 5 % ammonia acetate) followed by analyzed on a UPLC-MS/MS system (AJS ESI positive mode) equipped with a Capcell Pak C₁₈(250 mm×2.0 mm, MGII 5 μm) column with the mobile phase of acetonitrile and aqueous solution of ammonium acetate (20 mmol/L) containing formic acid (0.1 %) as the additive. Under optimized conditions, the linear range for codeine and morphine were 5.0~50.0 μg/L, and those for cocaine and papaverine were 1.0~20.0 μg/L, with relative coefficients above 0.999. The limits of detection for the method was in the range of 0.1~0.8 μg/kg, and average spiking recovery was in the range of 76.0%~111.2 % with RSDs below 10%.