This study focuses on weathering of granitic minerals by the bacteria Bacillus subtilis, especially how the ubiquitous soil bacterium Bacillus subtilis weathers granitic minerals through image analysis of mineral surface, and which mineral in the granite is the most vulnerable to weathering in a bacterial circumstance through comparison of using rock and single minerals analysis. Laboratory experiments reveal three basic conclusions: (i) Bacteria enhance weathering of granite and its constituent minerals by making pits on the mineral surface; (ii) The plagioclase is the most vulnerable mineral in bacteria-bearing granite. In the mineral experiments, albite (plagioclase group) is the most vulnerable in bacterial experiment; (iii) The orders of normalised pit-area ratio and pit density in bacteria-hearing granite are in accorded with the traditional weathering-series; this accordance suggests that bacterial weathering may have a large effect as biochemical weathering process.