An incubation experiment was conducted to estimate redox buffer capacity of "water-rock-microbe" interaction systems in sedimentary rocks. The water chemistry, microbial growth and community structure were analyzed during the incubations. The dissolved oxygen (DO) concentrations and oxidation-reduction potential (ORP) values decreased notably in the presence of active microorganisms, whereas abiotic reactions did not lead to reducing conditions during incubation. The change in microbial community structure suggests that nitrate-reducing and sulfate-reducing bacteria played an important role in reduction of water by using lignite-derived organic matter. These results show that the microbial role is extremely important for the redox buffering capacity in sedimentary rock environments.