BACKGROUND : Recurrent respiratory tract infection (RRTI) is a disease occurred frequently in preschool children. METHODS : A total of 120 RRTI children were randomly divided into active group, remission group, intervention group and control group, meanwhile 30 healthy children were selected as the healthy group. Children in the intervention group were given oral Bifidobaeterium tetravaccine tablets (Live) for 2 months, while the control group received routine treatment. Stool sample were detected to analyze the bacterial strains. The occurrence of respiratory tract infection (RTI) was compared between different groups during 1 year follow-up. RESULTS : Compared with the healthy group, the number of Bifidobacteria and Lactobacilli in the active group, remission group, intervention group and control group was significantly decreased (P < 0.05). The number of Bifidobacteria and Lactobacilli in the intervention group was significantly higher compared to other RRTI groups (P < 0.05). During the follow-up period, the average annual frequency of different acute RTI and use of antibiotics were significantly reduced (P < 0.05), the average duration of cough, fever and use of antibiotics at each episode were also significantly shortened (P < 0.05) in the intervention group compared to the control group. CONCLUSIONS : Children with RRTI are susceptible to intestinal flora imbalance. Oral probiotics can effectively improve the RRTI intestinal microecological balance in children and reduce the frequency of RTI.