Abstract: The mass fraction of free cresol content in tricresyl phosphate has been determined using the high performance liquid chromatography (HPLC). The samples were separated and detected by HPLC with the external standard method, the optimum chromatographic conditions were obtained. The experimental results showed that the best chromatographic conditions were: a C18 column (250 mm×4.6 mm×5 μm), methanol and water as the mobile phase (volume ratio is 8∶2), the flow rate: 1.0 mL/min, detected by an UV detector, with a detection wavelength of 280 nm, the column temperature of 35 ℃, and an isocratic elution and injection volume of 10 μL. The recovery was 95.9%~98.9%, and the relative standard deviation was 1.02%~2.55%. The method has the characteristics of simple, fast and high accuracy.