Objective To investigate the expression of mismatch repair protein (MMR) and programmed death ligand 1 (PD-L1) in endometrioid adenocarcinoma (EEC) and their relationship with prognosis. Methods From January 2015 to September 2020, 90 endometrioid adenocarcinoma tissues, 30 endometrium atypical hyperplasia tissues, 10 atypical accessory tissue and 30 paracancerous tissues were collected from Department of Pathology of Weifang People's Hospital of Shandong Province. The expression of MMR, PD-L1 was detected by immunohistochemistry. And Analyzed MMR, PD-L1 and the patient clinical pathology characteristic relevance and prognosiswere analyzed.Results MMR deletions (deficient MMR, dMMR), PD-L1 were higher in EEC tissues than in atypical hyperplasia tissues and control groups (Inspection level＜0.017). dMMR, PD-L1 were not related to FIGO staging, age, lymph node metastasis, and muscle infiltration depth of EEC patient (P＞0.05). The expression of PD-L1 was upregulated in the G3 phase compared with the G1 phase (Inspection level＜0.017). PD-L1 was positively correlated with dMMR (〖WTBX〗P〖WTBZ〗＜0.05). dMMR, PD-L1 were related to patient prognosis, of which dMMR, PD-L1 positive patients had a worse prognosis. MMR could be used as an independent factor affecting the survival of EEC patients (P＜0.05). Conclusion dMMR, PD-L1 play a synergistic role in the occurrence and development of EEC. Absence of MMR and PD-L1 are related to prognosis of patients. dMMR is an independent factor affecting the prognosis of EEC, and the combined detection of MMR and PD-L1 may provide a theoretical basis for the prognosis assessment of EEC