Objective:To analyze the clinical characteristics and prognosis of patients with myelodysplastic syndrome (MDS) with a bone marrow nucleated erythroid cell proportion of greater than or equal to 50% (MDS-E) .Methods:The clinical characteristics and prognostic factors of patients with MDS-E were retrospectively analyzed by collecting the case data of 1 436 newly treated patients with MDS diagnosed in the Institute of Hematology and Blood Diseases Hospital, Chinese Academy of Medical Sciences from May 2014 to June 2023.Results:A total of 1 436 newly diagnosed patients with complete data were included in the study, of which 337 (23.5%) patients with MDS-E had a younger age of onset and lower neutrophil and platelet counts compared with those in patients with an erythroid cell proportion of less than 50% (MDS-NE) (all P<0.05). The proportion of MDS cases with ring sideroblasts (MDS-RS) was higher in the MDS-E group than in the MDS-NE group, and multi-hit TP53 mutations were more enriched in the MDS-E group than in the MDS-NE group (all P<0.05). Among patients with MDS-RS, the frequency of complex karyotypes and the TP53 mutation rate were significantly lower in the MDS-E group than in the MDS-NE group (0 vs 11.9%, P=0.048 and 2.4% vs 15.1%, P=0.053, respectively). Among patients with TP53 mutations, the frequencies of complex karyotypes and multi-hit TP53 mutations were significantly higher in the MDS-E group than in the MDS-NE group (87.5% vs 64.6%, P=0.003 and 84.0% vs 54.2%, P<0.001, respectively). Survival analysis of patients with MDS-RS found that the overall survival (OS) in the MDS-E group was better than that in the MDS-NE group [not reached vs 63 (95% CI 53.3-72.7) months, P=0.029]. Among patients with TP53 mutations and excess blasts, the OS in the MDS-E group was worse than that in the MDS-NE group [6 (95% CI 2.2-9.8) months vs 12 (95% CI 8.9-15.1) months, P=0.022]. Multivariate analysis showed that age of ≥65 years ( HR=2.47, 95% CI 1.43-4.26, P=0.001), mean corpuscular volume (MCV) of ≤100 fl ( HR=2.62, 95% CI 1.54-4.47, P<0.001), and TP53 mutation ( HR=2.31, 95% CI 1.29-4.12, P=0.005) were poor prognostic factors independent of the Revised International Prognostic Scoring System (IPSS-R) prognosis stratification in patients with MDS-E. Conclusion:Among patients with MDS-RS, MDS-E was strongly associated with a lower proportion of complex karyotypes and TP53 mutations, and the OS in the MDS-E group was longer than that in the MDS-NE group. Among patients with TP53 mutations, MDS-E was strongly associated with complex karyotypes and multi-hit TP53 mutations, and among TP53-mutated patients with excess blasts, the OS in the MDS-E group was shorter than that in the MDS-NE group. Age of ≥65 years, MCV of ≤100 fl, and TP53 mutation were independent adverse prognostic factors affecting OS in patients with MDS-E.