Diatom microalgae represent the most abundant source of mesoporous biosilica in our planet. Their fossil derivative, diatomaceous earth (DE), consisting of diverse algal debris with nanostructured morphologies, is envisaged as a low cost silica support for biological applications. Intriguing features such as high surface/volume ratio and biocompatibility as well as unique absorption and confinement properties, make DE a suitable mesoporous support for biomolecules’ immobilization and stabilization. In this work, the model enzyme laccase was immobilized on DE using a polydopamine (PDA) coating that entraps a layer of protein molecules weakly interacting with DE. The DE/PDA/Laccase material, produced in aqueous solution under mild environment-friendly conditions, was characterized by spectroscopy and microscopy. The kinetic parameters and the recycle of the laccase were evaluated. This new hybrid material is in principle suitable for biomedical applications and for bioremediation in different environments.