MnIIICl–salen complex of tetradentate Schiff base ligand was incorporated into layers of clay montmorillonite by using an in situ flexible ligand method. The obtained modified clay was examined by X-ray diffraction, FT-IR and by using a cavity microelectrode (CME) to perform the electrochemical studies of the catalyst in the supported solid phase. Experiments show a well-defined and chemically reversible redox system of the manganese complex incorporated into the clay, similar to that observed in solution but with apparent diffusion coefficient around 2.3×10−9 cm−2 s−1. Dioxygen activation in catalytic conditions that was found to be efficient in the modified material is studied with the CME. It demonstrates the absence of formation of μ-oxo dimers and peroxo-bridged compounds and a good penetration of the different reactants into the clay. Moreover, this analysis illustrates the interest of CME as a powerful tool for the study of similar supported catalyst implying the biomimetic activation of molecular oxygen.