A H-point standard addition method (HPSAM) was applied to simultaneously determinate chlorate and bromate in ammonium perchlorate. The method is based on the difference between their reaction rates with chloride in acidic media whereby methyl orange is used as spectrophotometric indicator. The reaction can be monitored spectrophotometrically by measuring the decrease in the absorbance of methyl orange at 507 nm in the time range 50–250 s after initiation of the reaction with 1 s intervals. The results showed that chlorate and bromate can be determined simultaneously in the range 50–1000 and 50–2000 ng mL−1, respectively. The proposed method was applied to determinate chlorate and bromate impurities in military grade ammonium perchlorate. In addition, excellent agreement between this proposed method and standard methods was observed.