Objective:To explore the status of microsatellite instability (MSI) and its relationship with clinicopathological characteristics of patients with endometrial carcinoma.Methods:The clinical data of 365 patients with endometrial carcinoma who received surgery in Shanxi Province Cancer Hospital between January 2020 and December 2021 were retrospectively analyzed. Immunohistochemistry was used to detect the expressions of 4 DNA mismatch repair (MMR) proteins (MLH1, MSH2, MHS6, and PMS2), estrogen receptor (ER), progesterone receptor (PR), and p53 mutant protein in postoperative cancer tissue samples from 365 patients with endometrial carcinoma. All patients were divided into MSI group (1 or more non-expression of MMR protein) and microsatellite stability (MSS) group (4 proteins were all expressed), and the clinicopathological characteristics of patients in both groups were compared. φ efficient was used to analyze the correlation of MSI with ER, PR, p53 mutant protein expressions. Results:There were 72 cases (19.7%) in MSI group and 293 cases (80.3%) in MSS group; and the age of all patients was (53±19) years (21-83 years). There were statistically significant differences in the proportion of MSI patients in endometrial carcinoma patients with different age [>50 years vs. ≤50 years: 22.1% (61/276) vs. 12.4% (11/89)], tumor diameter [≤2 cm vs. > 2 cm: 25.9% (30/116) vs. 16.8% (42/249)], International Federation of Gynecology and Obstetrics (FIGO) staging [stage Ⅲ-Ⅳ vs. stage Ⅰ-Ⅱ: 31.1% (14/45) vs. 18.1% (58/320)], histological type [type Ⅰ vs. type Ⅱ: 21.7% (71/327) vs. 2.6% (1/38)] (all P < 0.05). There were no statistically significant differences in the proportion of MSI patients with different depth of invasion, degree of differentiation, lymph node metastasis, vascular involvement, and lesion location (all P > 0.05). Among 327 cases of type Ⅰendometrial carcinoma, 1 case was mucinous adenocarcinoma (MSS status), and the other 326 cases were endometrioid adenocarcinoma. Of the 72 patients with MSI, 71 cases were endometrioid carcinoma and the other was 1 of 3 mixed carcinomas in type Ⅱ endometrial carcinoma. There was a negative correlation between MSI and mutant p53 ( φ coefficient was -0.11, P = 0.031), and φ coefficient of the correlation of MSI with ER and PR was -0.03 and -0.06, while there were no statistically significant differences ( P value was 0.578 and 0.255, respectively). Conclusions:Endometrioid adenocarcinoma is the main type of endometrial cancer patients with MSI. MSI in endometrial cancer is correlated with age, FIGO staging, tumor diameter and histological type of patients, while negatively correlated with mutant p53.