Biofuel cells capable of converting glucose into electricity are of significant importance for the powering of medically implantable devices and for use with sugar rich agricultural waste. However, two large problems need to be tackled before these cells are of commercial value: enzyme stability and power density. Both of these must be improved to ensure an adequate working lifetime and power of devices. To tackle down these two problems, we prepared glucose oxidase electrodes using nanostructured materials such as carbon fibers and carbon nanotubes. Our preliminary experimental results in biofuel cells will be discussed in this presentation, such as optimum glucose concentration, mediator concentration, feed flow rate, operating temperature, and buffer type and concentration.