Abstract: A method for the determination of pyrogallol by spectophotometry was proposed based on the surface plasmon resonance absorption of the silver nanoparticles (AgNPs) that derived from modified silver mirror reaction. AgNPs were produced from the reduction of silver ammonia solution at room temperature in the media of sodium hydroxide and ammonia solution, with Tween-20 as dispersant and pyrogallol as reducing agent. The formation of AgNPs results in the colorless solution turned yellow with an absorption peak at 410 nm due to the surface plasmon resonance absorption of AgNPs. A linear relationship was found between the absorbance with the concentration of pyrogallol in the range of 3.96×10-7-2.38×10-5mol·L-1, with detection limit (3σ) of 2.97×10-7mol·L-1 and the molar absorption coefficient of 5.483×104L·mol-1·cm-1. The proposed method was applied to the determination of pyrogallol in industrial waste water, giving results in consistent with those obtained by normal spectrophotometry, with RSDs (n=5) less than 5.0% and recovery rates obtained by standard addition method in the range of 95.4%-104%.