In this paper, a potentiostat designed and implemented by field programmable gate array (FPGA) is proposed for electrochemical biosensors. Taking advantage of the FPGA, whose circuit modules can be concurrent executed in parallel, the proposed potentioatat’s performance designed by FPGA can be more efficient than any other potentioatat’s performance designed by microprocessor. This feature of FPGA is very important for the implanted application, i.e., Dopamine scan for Parkinson’s disease, because it needs high speed signal scan and high speed current measurement.