In this work, hydrothermal decomposition of [Fe(CN)6]3− in alkaline solution was conducted in a batch-type autoclave. The initial concentration of CN in [Fe(CN)6]3− in the sample solution was set to correspond to 1,000 mg CN/dm3. The experiments were conducted at temperatures of 403-443 K under O2 atmosphere at 0.1-4 MPa pressure. Hydrogen peroxide (H2O2) was used as an oxidation agent to enhance oxidative decomposition of [Fe (CN)6]3−. Moreover, the mechanism of this reaction was discussed. Results show that the rate of hydrothermal decomposition of [Fe (CN)6]3− is independent of O2 partial pressure. The rate is sufficiently described by first-order reaction Kinetics with respect to the [Fe(CN)6]3− concentration. The principal reaction products of cyanate (OCN−), formate (HCOO−), and ammonium (NH4+) ions were detected using ion chromatography. When H2O2 was added to [Fe(CN)6]3− solution, the decomposition rate of CN in [Fe(CN)6]3− at the initial stage of the reaction (0.5-2 h) was found to be 1.2-1.3 times higher than that without H2O2. The reaction products of HCOO−, carbonate (CO32−) and NH4+ ions were detected. Such different reaction products resulting from H2O2 addition suggest the formation of CO32−and N2 during oxidative decomposition of [Fe(CN)6]3− by H2O2.