Germplasm resources of homoacetogens are not only the basis for the production of chemical solvent acetic acids but also important for investigating their ecophysiological functions in anaerobic digestion systems. With CO₂ as the carbon source, an anaerobic bacterium strain CA3 was isolated from the anaerobic activated sludge by the modified Hungate anaerobic technique. The strain CA3 is a strictly anaerobic, gram-positive and oval-shaped acetogenic bacterium. This bacterium could metabolize H₂/CO₂ to acetate, and was able to ferment glucose and fructose with acetate as a major product. The phylogenetic analysis based on 16SrRNA gene sequence indicates that the strain CA3 affiliates to the genus Blautia sp.. This strain could grow with temperature in the range from 20℃ to 45℃. With the optimum temperature of 35℃ and the initial pH value of 8.0, an acetate producing rate of 8.92mg/(L·h) was obtained in its pure culture with H₂/CO₂ as the carbon source. The most feasible nitrogen source for the strain CA3 to ferment glucose is the yeast extract and the acetate producing rate reaches 1370mg/L in its pure culture.