The authors describe the preparation of Fe₂(MoO₄)₃ materials with micrometer dimensions, and show that they are highly efficient peroxidase mimics that can be used in a photometric assay for H₂O₂. Depending on the experimental conditions of synthesis, the Fe₂(MoO₄)₃ micromaterials display different morphologies, surface properties, and peroxidase-like activities. Among them, Fe₂(MoO₄)₃ with flower-like structure has the largest BET specific surface area and the most negative potential. It exhibits the best peroxidase mimetic activity in catalyzing the oxidation of 3,3′,5,5′-tetramethylbenzidine in the presence of H₂O₂ to generate a blue-green product. Based on these findings, method was worked out for H₂O₂ determination that allows both visual and photometric read-out. The assay has a detection limit as low as 0.7 μM, is selective and practical. Given its sensitivity, the method has a good potential with respect to determination of H₂O₂ in clinical samples but also in oxidase-type of reactions where H₂O₂ is being produced.