Microperoxidase-8, a small, peroxidase-type enzyme was successfully immobilized into nanoparticles of the mesoporous and ultra-stable . The immobilized enzyme retained fully its catalytic activity and exhibited enhanced resistance to acidic conditions. The biocatalyst was reusable and showed a long-term stability. By exploiting the properties of the MOF's framework, we demonstrated, for the first time, that the MOF matrix could act in synergy with the enzyme (Microperoxidase-8) and enhance selectivity the oxidation reaction of dyes. The oxidation rate of the harmful negatively charged dye (methyl orange) was significantly increased after enzyme immobilization, most likely due to the preconcentration of the methyl orange reactant due to a charge matching between this dye and the MOF.Enzymes are biomolecules with remarkable catalytic properties essential for specific applications, such as production of biochemicals and biofuels, and for biosensing and bioremediation purposes. [1] Despite many advances in enzyme engineering, they remain expensive and/or fragile entities. As a result, their use in industrial context often requires their immobilization on a solid support to increase their stability and recovery. Many supports have been developed in the last decades, including, but not limited to, biopolymers/synthetic polymers, sol-gel materials, mesoporous silica, carbon materials, [2] and recently Metal-Organic Frameworks (MOFs). [3] These latter are a class of crystalline hybrid porous materials characterized by a vast chemical functionality, exhibiting a large variety of structural features (surface area, pore size, shape, flexibility…). These have sparked a great interest in many applications such as gas storage and separation, heat transfer, biomedicine, sensing and catalysis, among others. [4] As immobilization matrices, they seem promising since the