OBJECTIVE:To establish a method for the determination of related substance in posaconazole raw material.METHODS:HPLC method was adopted.The separation was performed on Zorbax Eclipse Plus C18 column with mobile phase consisted of 0.05 mol/L ammonium acetate solution (pH adjusted to 4.0 using acetic acid)-acetonitrile (gradient elution) at the flow rate of 1.0 mL/min.The detection wavelength was set at 262 ran,and the column temperature was 30 ℃.The sample size was 20 μL.RESULTS:The linear range of intermediate I was 0.05-5.0 μg/mL (r=0.999 9);the limit of quantitation was 0.05 μg/mL,the limit of detection was 0.013 μg/mL;RSDs of precision test,stability test and repeatability test were lower than 2.0％;the recoveries was 98.00％-101.69％ (RSD=1.22％,n=9).CONCLUSIONS:The method is simple,accurate and suitable for the determination of related substance in posaconazole raw material.