Recent progress in the synthesis of nano-structured materials having desirable physico-chemical properties has opened the door for the fabrication of more sensitive and stable biosensors. In this chapter, we will describe the use of ordered mesoporous carbons (OMCs) as matrix materials for enzymebased biosensors. The unique characteristics of OMCs, including large pore size and surface area, enabled a high loading of biocatalyst, which is a major requirement of sensitive biosensors. Another useful feature, magnetism, was added to produce a high-capacity magnetic enzyme carrier by incorporating magnetic nanoparticles into the OMC. Enzymes immobilized in the magnetic OMC were used to construct a magnetically switchable electrochemical biosensing system in which the catalytic electron flow can be controlled by a magnetic force.