Abstract: The waterborne coating sample (1.000 g) was extracted ultrasonically for 20 min with about 20 mL of 1% (φ, the same below) acetic acid methanol solution. After cooling to room temperature, the solution was made up to 25.0 mL with 1% acetic acid methanol solution. After shaking up, the solution was centrifugated for 20 min at the speed of 2 000 r·min^-1, and then the supernatant was filtered with 0.45 μm organic phase filter. HPLC was applied to the determination of 4 biocides, i.e. carbendazim, diuron, chlorothalonil and triclosan in the filtrate. Agilent ZORBAX SB-C₁₈ chromatographic column was used for separation with mixtures of methanol and 0.3% (volume fraction) ammonia with different mixing ratios as mobile phase in the gradient elution. Detection at 236 nm was adopted in the determination. Linear relationships between values of peak area and mass concentration of the 4 biocides were kept in the same range of 0.4-40.0 mg·L^-1, with detection limits (3S/N) in the range of 0.47-1.10 mg·kg^-1. Values of recovery found by standard addition method were in the range of 92.5%-106%, and values of RSDs (n=7) of recovery amounts were in the range of 0.43%-2.8%.