In this paper, the effects of contacted sulfate-reducing bacteria(SRB) and metabolites(with molecular weight in the scales of 0~200, 200~2000, 2000~10000, respectively) on the reductive decomposition of gypsum were investigated, and the results showed that:① in bacterial experiments, SRB produced more alkalinity, which led to the increase of pH values; ② the decomposition of gypsum became stronger with the strengthening of the contact; ③ SRB and metabolites induced the formation of carbonates, including well crystallized calcite and amorphous carbonates; under suitable conditions, metabolites could also constrain the decomposition of gypsum. It is inferred that the adhesion of SRB and metabolites on gypsum has a significant effect on mineral decomposition. Two mechanisms can be used to explain such process:complexation between organic groups and Ca²⁺ in gypsum, and construction of microenvironment by contacted SRB with high pH and HCO₃^-.