Upregulated delta-like protein 3 (DLL3) functions as a Notch ligand and has been a target for cancer therapy. The present study assessed DLL3 expression as a tumor marker for endometrial cancer.RNA-Seq expression data and clinicopathologic records from 545 patients with endometrial cancer were downloaded from The Cancer Genome Atlas database. Mann-Whitney U and logistic regression tests were applied to associate the level of DLL3 expression with clinical variables from the patients. Kaplan-Meier curves and log-rank tests were performed to compare overall survival of patients stratified by different levels of DLL3 expression. Multivariate Cox regression tests were used to analyze independent predictors for endometrial cancer. DLL3 expression was upregulated in endometrial cancer tissues compared to para-carcinoma tissues (P = .0003). High DLL3 expression was associated with the age of patients (odds ratio [OR] = 1.74), advanced stages of the International Federation of Gynecology and Obstetrics system (OR = 2.9), grade III/IV (OR = 5.1), myometrial invasion (OR = 2.2), pelvic involvement (OR = 12.9), and para-aortic lymph node metastasis (OR = 9.9) (all P ≤ .001). Furthermore, upregulated DLL3 expression was also associated with a median overall survival of 112 months (HR = 1.85, confidence internal 1.202-2.846, P = .005). The multivariate analysis showed that DLL3 overexpression and advanced tumor stages, grades, and lymph node metastases were all independent prognostic predictors for endometrial cancer.The DLL3 expression could be a potential and novel tumor marker for early diagnosis and an independent predictor of poor survival for patients with endometrial cancer.