Abstract: Based on prismatic spectrophotometry, a method for determining ruthenium content on activated carbon-supported ruthenium catalyst for ammonia synthesis was studied. Under the conditions of acid and ethanol, a blue product was obtained by Ru (Ⅲ) and thiourea, which, with maximum absorption wavelength at 620 nm, can determine the ruthenium content in catalyst. The result showed that with the easy-to-operate method, the relative standard deviation ranges from 1% to 3% and the recovery ratio from 97.5 % to 102.0 %. This method could rapidly and accurately determine the content of ruthenium on Ru/AC catalyst for ammonia synthesis.