Objective To investigate the clinical diagnostic value of the endothelial glycocalyx injury biomarker syndecan-1 (SDC-1) for necrotizing enterocolitis (NEC) in preterm infants. Methods A multicenter, prospective study was conducted from February to July 2025 at the First Affiliated Hospital of Army Medical University, Sichuan Maternal and Child Health Hospital, and Liaocheng People's Hospital. Preterm infants with Bell stage Ⅱ-Ⅲ NEC were enrolled as the NEC group (n=38), and contemporaneous non-NEC preterm infants were selected in a 1∶1 ratio as the non-NEC group (n=38). Perinatal data and measurements of complete blood counts, SDC-1, and high-sensitivity C-reactive protein (hs-CRP) were collected. Multivariable logistic regression was used to evaluate risk factors for NEC. Receiver operating characteristic (ROC) curves were used to assess diagnostic performance of SDC-1. Results Neutrophil count, SDC-1, and hs-CRP levels were significantly higher in the NEC group than in the non-NEC group (P<0.05), while platelet count was significantly lower (P<0.05). Elevated SDC-1 (OR=1.081, 95%CI: 1.028-1.137; P<0.05) and hs-CRP (OR=1.267, 95%CI: 1.051-1.527; P<0.05) were independent risk factors for NEC. ROC analysis showed that SDC-1 (cutoff 125 ng/mL) and hs-CRP (cutoff 6.56 mg/L) yielded areas under the curve (AUCs) of 0.882 and 0.863, respectively. Their combination achieved an AUC of 0.938 with a sensitivity of 76.3% and a specificity of 97.4%. Conclusions SDC-1 is a potential biochemical biomarker for diagnosing NEC in preterm infants, but its clinical utility requires further validation in larger-sample studies.