The aim is to establish a method for determination of related substances of benzaldehyde and toluene in benzoic acid crude drug.RP-HPLC method was adopted.The determination was performed on WondasilTM-C18 column with mobile phase of methanol-0.02 mol/L ammonium acetate(pH 4.0)(80:20) at flow rate of 0.5 mL/min.Detection wavelength was set at 254 nm.Benzoic acid, benzaldehyde and toluene could be separated completely.Linear range of benzaldehyde and toluene was 2.0-7.2μg/mL(r=0.999 5) and 1.75-6.30μg/mL(r=0.9989) resp.Detection limits were 0.05μg/mL and 0.2μg/mL.Average recoveries were 100.57%(RSD=0.99%, n=9) and 99.58%(RSD=0.86%, n=9), resp.This method was sensitive and accurate, and it could be used for simultaneous determination of related substances of benzaldehyde and toluene in benzoic acid crude drug.