Lactobacilli strains are Gram-positive, non-spore, catalase-negative rods bacteria that have an important ecological role in the digestive tract including Production of antimicrobial substances, Enhance the immune response and Increase nutrient availability. To identify lactobacilli in the gut of  Rutilus frisii kutum fish, 40 fish were randomly catch from the Caspian Sea. The samples under sterile conditions and ice transferred to microbiology in Tabriz Branch Islamic Azad university and After phenotypic and biochemical test, Lactobacillus samples to make a diagnosis based on the molecular structure of the gene for srDNA 16, DNA extracted and take action to identify lactobacilli with specific primers and Then for the early identification of species, Taq1 restriction enzymes were used. Then three different samples for sequencing were sent for diagnosis. The results of sequencing showed that 99-97% sequence similarity to the gene sequence database for the species Lactobacillus fermentum SrDNA 16 recorded. Just one example of the similarity of 89% of the species Lactobacillus fermentum the sample for sequencing as partial was sent. After sequencing the gene number JQ906262 as Lactobacillus sp. RU1 16S ribosomal RNA gene, partial sequence was recorded on ncbi.