Abstract: A method of ultra performance liquid chromatography-mass spectrometry (UPLC-MS) was established for the determination of octylphenol ethoxylates and nonylphenol ethoxylates in six kinds of liquid organic pesticides formulations (emulsifiable concentrate, microemulsion, suspension concentrate, emulsion in water, soluble concentrate and aqueous solutions). The samples were ultrasonic extracted and diluted with methanol，then separated by Waters BEH C18 column (2.1 mm×100 mm×1.7 μm) with 10 mmol/L ammonium acetate and methanol as mobile phase, gradient elution and column temperature of 30 ℃, while the flow rate was 0.3 mL/min. Quantification was performed in selected ion record (SIR) mode using Quattro Premier XE mass spectrometer with positive ion mode of electrospray ionization. The results showed that the octylphenol ethoxylates (OPEO) and nonylphenol ethoxylates (NPEO) in the concentration range of 50-10 000 μg/L have good linear relationships (r>0.999). The recoveries at three spiked levels (5, 20, 100 mg/kg) are 81.8%-115.5% (n=8) with the relative standard deviation of 1.1%-9.8% (n=8), and the limit of quantitative is 50 μg/L. The method is simple, rapid, accurate, and which is suitable for qualitative analysis and quantitative detection of alkylphenol ethoxylates additives in organic pesticides.