Abstract: It was found that in H2SO4 medium, the oxidation of neutral red by hydrogen peroxide was strongly inhibited by the presence of Ru(Ⅲ). Based on this fact, the determination of traces of Ru(Ⅲ) by inhibitory kinetic photometry was proposed. The optimized conditions found were as follows: ① amount of 0.01 mol·L-1 KIO4 solution: 1.40 mL; ② amount of 1×10-3mol·L-1 methyl green solution: 1.50 mL; ③ temperature of reaction: 80 ℃; ④ time of reaction: 10 min. Linear relationship between values of ΔA and mass concentration of Ru(Ⅲ) was obtained in the range of 0.04-64 μg·L-1. Detection limit (3s/k) of the method found was 8.5 ng·L-1. The proposed method was applied to the determination of Ru(Ⅲ) in samples of active carbon and molecular sieve. Recovery was tested by addition of standard solution to samples, giving values of RSD′s (n=6) and recovery ranged from 1.6%-2.2 % and 98.6%-100% respectively.