Abstract: UPLC-MS/MS was applied to the determination of amoxicillin residue in water. After being filtered through PTFE needle type filter, the water sample was separated on a Kinetex 2.6 μm C18 chromatographic column with a mixture of 0.01% (φ) formic acid solution and acetronitrile as mobile phase for gradient elution. ESI+ and MRM were adopted in MS analysis, and external standard method was used for quantification. Linear relationship was found between the peak area and the mass concentration of amoxicillin the range of 0.020-1.50 μg·L-1, with the detection limit (3S/N) of 10 ng·L-1 and the lower limit of determination (10S/N) of 20 ng·L-1. Recovery rates obtained by standard addition method were in the range of 91.3%-105% and RSDs (n=6) were less than 6.0%.