Abstract： Objective:To investigate the efficacy and pregnancy outcome of fertility-preserving treatment for patients with stage Ⅰa, grade 2 endometrial cancer (EC).Methods:Clinical data was retrospectively collected for EC or atypical endometrial hyperplasia (AEH) patients treated in Peking University People's Hospital, Foshan First People's Hospital of Guangdong Province and First Affiliated Hospital of Sun Yat-sen University, from 2010 to 2019. Inclusion criteria for fertility-preserving treatment included: (1) Age ≤45 years. (2) EC with histological differentiation of G 1, G 2 or endometrial AEH. (3) EC disease should be stage Ⅰa, confined to the endometrium without myometrial invasion, lymph node or extrauterine metastasis. Treatment regimen: patients were given oral progestin therapy and endometrial pathology was evaluated every three months. Patients were divided into three groups as G 2 EC group, G 1 EC group and AEH group based on the histological differentiation. Oncological and pregnancy outcomes were compared among them. Results:(1) Totally 57 eligible patients were included in this study, including 11 cases with G 2 EC, 22 cases with G 1 EC, and 24 cases with AEH. (2) Oncological outcome: among the three groups of G 2 EC, G 1 EC and AH, the complete remission rates (9/11, 91% and 96%, respectively) and recurrence rates (3/9, 30% and 22%, respectively) were not significantly different (all P>0.05). Median remission time was significantly longer in the G 2 EC group than those in the other two groups (8, 6 and 4 months; P=0.046). Among 9 G 2 EC patients who recurred after complete remission, three patients relapsed at 7, 18 and 53 months, respectively. All 3 patients chose fertility-sparing treatment again, and all achieved complete remission after retreatment. (3) Pregnancy outcome: among the three groups, the assisted reproduction technology rates (4/8, 5/18 and 36%, respectively) and pregnancy rates (6/8, 5/18 and 36%, respectively) had no significant difference ( P>0.05). However, time interval to pregnancy was shorter in G 2 EC patientsthan the other two groups (4, 9 and 22 months, respectively; P=0.006). Conclusions:Fertility-preserving treatment for patients with stageⅠa, G 2 endometrial cancer, may obtain a relatively high remission rate and an acceptable pregnancy rate. However, further exploration is needed due to the limited number of cases.