A bacterial strain producing conjugated linoleic acid was isolated from the goat rumen in Erdos, Inner Mongolia, the strain was designated as RB111. CLA production by the strain reached 269.2 mg/L, in which the percentage content of cis9, trans11-CLA accounted for 52.64% and that of trans10, cis12-CLA accounted for 47.36%. The strain RB111 was identified using its morphological characteristics, fatty acid composition and physiological and biochemical properties, as well as its 16S rRNA gene sequence. The strain RB111 shares 99% sequence identity with the type strain NCDO 599^T of Streptococcus infantarius. The result of fatty acid composition analysis revealed that the major fatty acids present in the strain RB111 were C16:0, C18:1 ω9c and C18:0, the total account of the three kinds of fatty acids was 60.64%. The morphological characteristics and the results of physiological and biochemical properties of the strain were in well agreement with that of the type strain NCDO 599^T of Streptococcus infantarius. On the basis of these data, the strain RB111 was definited to Streptococcus infantarius.