Objective To study the predictive value of umbilical cord blood regulatory T cells (Treg) for bronchopulmonary dysplasia (BPD) in preterm infants. Method From June 2017 to December 2018, premature infants with gestational age less than 32 weeks admitted to NICU of our hospiatal were prospectively selected. The umbilical cord blood was collected at birth to examine the Treg amount. The infants were assigned into BPD group and non-BPD group according to the diagnosis at discharge. The differences of Treg amount between the two groups and different degrees of BPD were analysed. Result A total of 124 premature infants (GA<32 weeks) were admitted, including 41 cases in BPD group (mild, n=18;moderate, n=14; severe, n=9) and 83 cases in the non-BPD group. The BPD group had GA of (29.6 ± 1.1) weeks and birth weight (BW) of (1128 ± 135) g. The non-BPD group had GA of (29.8 ± 1.1) weeks and BW of (1316 ± 180) g. The birth weight, 1min and 5min Apgar scores in BPD group were lower than the non-BPD group (P<0.001). The BPD group had higher incidence of respiratory distress syndrome, longer duration of mechanical ventilation (MV) and oxygen inhalation(P<0.001) than the non-BPD group. The MV duration and oxygen inhalation duration in the severe BPD group were significantly longer than the moderate and mild BPD groups, and the duration in the moderate group was longer than the mild group (P<0.001). The number of Treg in cord blood in the BPD group [(1.43 ± 0.06) × 105 cells/ml] was significantly lower than the non-BPD group [(2.57 ± 0.09) × 105 cells/ml], and the difference was statistically significant (P<0.001). Multivariate Logistic regression analysis showed that a significant decrease in the number of Treg was a risk factor for BPD in premature infants (OR=0.000, 95％CI 0.000 ～ 0.012, P=0.009). The number of Treg in umbilical cord blood was negatively correlated with the severity of BPD. The area under the ROC curve showed that the cut-off value was 1.95 × 105 cells/ml, with Youden index 0.613, sensitivity 85.4％ and specificity 75.9％. Conclusion The number of cord blood Treg cells may be a useful biomarker for predicting BPD in premature infants.