In an early stage of the study, a DNA analysis found the presence of a strain, which is regarded as Xanthomonadaceae of Bacteroidales. Further DNA analysis by cloning found microorganisms which can be presumed to be Acetobacter and Gluconacetobacter. These analyses have shown high possibility of the presence of multiple microorganisms in corroded layers of ancient bronze mirrors. We are planning to cultivate the microorganisms, which live in unusual environment, but we have not found the appropriate medium for cultivating them. We presume that these microorganisms are causing corrosion in bronze objects. In further research, we hope to prove microbiological corrosion of ancient bronze objects.