Enzymatic biofuel cells have attracted attention. However, there are drawbacks to be overcome for practical applications: The lower output voltage and shorter life time. In this paper, I will present our recent progress in MEMS techniques-based challenge to these problems. The possible output voltage of a single biofuel cell is generally lower than 1 V. The series connection of biofuel cells requires a system for ionic isolation between each cell. We will report an automatic air-valve to connect biofuel cells in series based on the air-trapping at a lotus leaf-like superhydrophobic structure that is manufactured between fuel cells arrayed in a microfluidic channel. The lifetime of an operating enzymatic fuel cell is limited typically within one week. We have been developing the parallel-connected biological micro fuel cells, each of which is shielded from fuel solutions by using degradable materials such as PLGA.