Abstract: A rf-driven ion source has been developed for the ion beam bioengineering. As used in an electrostatic accelerator, the ion source was specially designed considering with the structure, weight and the power supplies. The size of the extracting electrode was calculated in detail. The extracting beam characteristics of the ion source depending on extracting voltage, focusing voltage and gas pressure were obtained by experiments. The variation of the beam radius along the axis was measured. Factors producing the beam instability were generally discussed, and effective techniques were used to reduce the beam instability. Experimental results showed that the extracting characteristics matched the theoretical expectation well. the maximum beam current was obtained when the extracting voltage was