We report the simple one-pot synthesis of magnetic nanoparticles coated with silica-gel layers that entrap laccase (Lc) by the water-in-oil microemulsion method. The amorphous porous structure of the silica layer enables the entrapped Lc to react with substrates in solution. The enzymatic activity is studied using Michaelis-Menten kinetics. The reusability of the magnetic nanoparticles is examined.