Objective To evaluate the efficacy and fertility outcomes of progestin treatment for complex atypical hyperplasia (CAH)/grade I endometrial cancer (G1EC) in Chinese patients (≤ 40 years old). Methods Women ≤ 40 years old who were treated with progestin for CAH or G1EC were identified from 9 provinces of China. The time to achieve complete response (CR) and the time from CR to recurrence or pregnancy were censored for patients without events and were analyzed for associations between patient and treatment characteristics. Results Thirty-two patients were included: 13 with CAH and 19 with G1EC. Nine patients exhibited elevated serum HbA1C before treatment. After a mean follow-up of 32.5 months, the CR rate was 84.4%. Patients who exhibited elevated HbA1C were more likely to experience CR, while those with polycystic ovarian syndrome (PCOS) exhibited the opposite outcome (p = 0.01, 0.03). Nine of 21 patients experienced clinical pregnancies. Eight patients underwent assisted reproductive technology (ART). Five patients had newborn infants. Patients undergoing ART were more likely to become pregnant (p = 0.04). Conclusion Oral progestin is an effective fertility-sparing treatment for women with CAH/G1EC in China. Patients with elevated HbA1C receiving both metformin and progestin were more likely to achieve CR, whereas those with PCOS were not. ART is a good choice for clinical pregnancy after treatment. © 2015 Published by Elsevier Inc.