Abstract: A HPLC method for simultaneous determination of benzalkonium bromide and o-phthalaldehyde (OPA) in quaternary ammonium compound salt disinfectant was established. 1.0 mL of the sample was made up to 10.0 mL with the mobile phasemixture composed of 0.02 mol·L^-1 acetic acid-ammonium acetate buffer solution (pH 4.5) and methanol in the volume ratio of 1:1 as dilution solvent. After mixing for 5 minutes by votex, the sample solution was passed through a 0.45 μm filter membrane, and the 2 analytes in the filtrate were determined by HPLC at the detection wavelength of 263 nm under conditions using XDB-C₁₈ column as stationary phase and isocratic elution with mobile phase. As found by results that linearity range of standard curves of benzalkonium bromide and OPA was found same in the range of 10.0-800.0 mg·L^-1, and detection limits of benzalkonium bromide and OPA were 5.0, 3.5 mg·L^-1, respectively. The 3 sample were analyzed by the above method, and results obtained were in conformity with the label values, with RSDs (n=7) of determined values lower than 1.0%. Recovery test was made by standard addition method using the 3 samples as matrixes at the 3 concentration levels, giving values of recovery of 93.7%-95.2% and 94.5%-98.5%, respectively.