Abstract: Objective：To study the relationship between respiratory tract Ureaplasma urealyticum (UU) colonization and bronchopulmonary dysplasia (BPD) in preterm infants. Methods：This is a retrospective cohort study. We enrolled hospitalized premature infants who received respiratory secretions test for UU. UU positives (colonization) and negatives were assigned to the exposure and non-exposure group, respectively. Discharge from NICU was taken as the end of the cohort. We observed the relationship between UU colonization in preterm infants and BPD. Preterm infants with UU colonization were divided into different subgroups according to the cut-off value of ROC curve between UU-DNA copies and the start time of antibiotic therapy. Results：A total of 399 preterm infants were included in the analyses with 105 cases (26.3%) of UU colonization and 294 cases of non-UU colonization. The gestational age and birth weight of infants with UU colonization were lower than those of infants in the control group. But the proportion of premature rupture of membranes and moderate or severe BPD were higher. After adjusting for several covariates, no significant relation was found in BPD between infants with UU colonization and infants without colonization. But UU-colonization might be related to higher oxygen demand (OR=4.22, 95%CI: 1.34-13.26). UU colonization with higher copies(≥4.47×105·mL-1), and treatment starting later than 8 days after birth were related to a higher incidence of BPD. Conclusion：Respiratory tract UU colonization is not significantly related to the risk of BPD in preterm infants. Late drug treatment and higher DNA copies may be risk factors for BPD.