Abstract: The content of peracetic acid (PAA) in disinfectant of PAA was determined by spectrophotometry with Fe²⁺-o-phenylenediamine (OPD) as chromogenic reagent. 0.25 mL of disinfectant solution was titrated to a stable pink with 0.01 mol·L^-1 potassium permanganate solution. An aliquot (5.00 mL) of sample solution was mixed with 10 g·L^-1 OPD solution, acetic acid-sodium acetate buffer solution (pH 1.5) and 0.01 mol·L^-1 Fe²⁺ solution in sequence. After reacting for 3 min at room temperature, the content of PAA was determined at 448 nm. The results showed that the apparent activation energy of the color reaction between OPD and PAA was reduced effectively by using Fe²⁺ as catalyst, and the color reaction could be completed within 3 min, with the molar absorption coefficient of the reaction system of 5.8×10³L·mol^-1·cm^-1; a linearity relationship between concentration of PAA and its respective absorbance was kept within 0.24 mmol·L^-1, with detection limit (3s/k) of 5.0×10^-3mmol·L^-1. The method was used for the determination of PAA content in disinfectant of PAA, and determined values were consistent with labeled values, with RSDs of the measured values (n=6) less than 2.2%. Recovery test was made by standard addition method using PAA disinfectant as matrix, giving recoveries in the range of 97.5%-105%.