Lynch syndrome (LS) is an autosomal dominant hereditary tumor syndrome characterized by tumors in the uterus and ovaries of female patients. Atypical endometrial hyperplasia (AH) or endometrial carcinoma (EC) in LS patients is caused by germline mutations. Few studies have analyzed the role of estrogen or the role of fertility-sparing therapies for these patients. Here we reported a LS patient who had AH and attempted to preserve her fertility under close monitoring and after multidisciplinary consultations. The lesion was completely reversed after 3 months of treatment with levonorgestrel-releasing intrauterine system (LNG-IUS), and no recurrence was noted during the 9-month follow-up. The possibility of LS should be considered in AH patients with a family history of relevant cancers. Meanwhile, for LS patients with complicated AH and a strong desire to retain infertility, fertility-sparing treatment may be attempted to reverse endometrial lesions under close monitoring and after adequate evaluation.