A bio-etching method using Thiobacillus ferrooxidans (T.f.) for processing micro-gear has been developed. The principle of bio-etching method is that certain microorganisms in nature consume some metal ions to be energy during their growth. The strain of Thiobacillus ferrooxidans consume elemental ferric and cooper ions as its energy source, so T.f. is selected as bio-etching tool, Leathen culture medium is selected as culture medium of T.f., and the thin copper sheet is used as the processed material. During the micro-gear is processed, firstly, thin copper sheet of 0.05mm is cleaned in the acid liquid and some materials such as dirt and grease are cleaned away, then, the anti-erode film is applied to the surface of thin copper sheet, then the surface of thin copper sheet is irradiated by ultraviolet under the condition that the surface is covered by mask film and developed, the anti-erode film that not covered by mask film will be dissolved and cleaned away, after that, thin copper sheet is put into the T.f. liquid and agitating, after the 3h, micro-gear is obtained. The result is showed that micro-gear can be processed by bio-etching method.