Diversity of sulfate-reducing bacteria, their substrates in the intestine, metabolism of molecular hydrogen, and their trophic relationship with other microorganisms were characterized. Mucosal bacteria of the colon and the role of intestinal microbiota in disease development were described. Microbial communities and hydrogen sulfide concentration in large intestine of healthy people and patients with ulcerative colitis were compared. A characterization of physiological and biochemical properties of intestinal sulfate-reducing bacteria, and their mechanisms of dissimilatory sulfate reduction in human and animal colon were described. The conception of the functional role of sulfate-reducing bacteria in the humans and animals intestine was created. It is based on the ability of these microorganisms form toxic metabolites that are a prerequisite development of colon diseases. Experimental data allow developing basic criteria for assessing the course of the inflammation process and to establish the level of risk of the disease in order to prevent it. These data can be also helpful for master students which study such courses as “General Microbiology”, “Medical Microbiology”, “Veterinary Microbiology”, “Physiology and Biochemistry of Microorganisms”, for microbiologists, physiologists, biochemists, gastroenterologists, physicians, experts in cell biology and for readers which are interested in study of inflammatory bowel disease including ulcerative colitis.