Abstract: objective To establish a HPLC method of simultaneous determination of methyl hydroxybenzoate ,propyl hydroxybenzoate and degradation product P-Hydroxybenzoic acid in oral liquid prepatations .method The Luna C18 was adopted to determinate assay with gradient elution, 0.1% phosphonic acid as the mobile phase A and acetonitrile as the mobile phase B. The detection wavelength was 254nm. Results methyl hydroxybenzoate,propyl hydroxybenzoate and P-Hydroxybenzoic acid were good linear in the range of24.02~72.02μg/mL,3.04~9.04μg/mL and 0.28~0.84μg/mL.The linear equation was A=90569C 122945(r=0.9999),A=86802C 15680(r=0.9999) and A=532.5C-498.6(r=0.9999) respectively. The average recoveries of methyl hydroxybenzoate propyl hydroxybenzoate, P-Hydroxybenzoic acid were 98.1% ,98.5% and 98.8% respectively. The detection limit of P-Hydroxybenzoic acid was 0.10 ng. Conclusion The method is simple and accurate. It can be used to detect methyl hydroxybenzoate ,propyl hydroxybenzoate and degradation product P-Hydroxybenzoic acid in oral liquid prepatations .