Abstract: FI-spectrophotometry was applied to the determination of activity of peroxidase in radish. The optimized conditions found were as follows: ① reaction temperature: 60 ℃; ② carrying solution: 0.05 mol·L-1 NaH2PO4-Na2HPO4 buffer solution (pH 5.5); ③ sampling volume: 40 μL; ④ length of reaction coil: 200 cm; ⑤ reaction reagent: mixture of 1.5 mmol·L-1 H2O2 and 3.5 mmol·L-1 2-guaiacol. Apparent molar absorptivity of 2-guaiacol found was 0.012 5 L·μmol-1·cm-1. Linearity range of horse radish peroxidase was found between 454-7 265 U·L-1 with detection limit (3s/k) of 7 U·L-1. Results of test for recovery of this method were found in the range of 94.2%-107%. Precision of the method was tested at the concentration levels of 500, 2 500 U·L-1 of horse radish peroxidase standard solution for 11 determination, values of RSD′s found were less than 0.62%.