Abstract: Content determination of sodium pyrosulfite in oxyclozanide suspension. Sulffur dioxide released from sodium pyrosulfite in solution can fade fuchsin acid solution. Absorbance was measured at the wavelength of 548 nm by colorimetric method and content sodium pyrosulfite was calculated by external standard method. Anhydrous sodium sulfite showed good linearity（R²=0.992）in the range of 9.49~94.90 μg/mL;The average recovery was 97.09% with RSD=0.641 1%. The method can effectively determine the content of the sodium pyrosulfite in the oxyclozanide suspension.

Key words: oxyclozanide suspension, sodium pyrosulfite, colorimetric method