The silicon removal from ultra-pure water by electrodeionization (EDI) is studied. The influences of applied voltage, pH values and flux during the EDI process on the silicon removal and the mechanism of the silicon removal by EDI in ultra-pure water are investigated. Moreover, the results of silicon removal by EDI are compared with those by traditional processes. These experimental results show: under conditions of the same pH values and flux, the efficiency of silicon removal can be improved by increasing EDI′s voltage; under conditions of the same voltage and flux, the efficiency of silicon removal increases firstly and then decreases a little with the pH values increasing; under conditions of the same voltage and pH values, it is not good for silicon removal to increase EDI flux.