Objective To study the effect of menopause status and the time of taking tamoxifen (TAM) on endometrial lesions after breast cancer surgery. Methods A total of 330 patients with postoperative vaginal irregular bleeding after breast cancer surgery or endometrial lesions after B ultrasonic from August 2007 to August 2017 in Northern Jiangsu People 's Hospital were retrospectively analyzed, including 180 cases of taking TAM treatment (medicine-taking group), and 150 cases of not taking TAM treatment (non medicine-taking group). The patients were also divided into the menopause group and the premenopausal group. According to the time of taking TAM, the patients were divided into < 2 years group, 2-5 years group and > 5 years group. Chi-square and Fisher test were used to compare the differences. Results The endometrial lesions incidence in the medicine-taking group was higher than that in the non medicine-taking group [84.44 ％ (152/180) vs. 56.00％(84/150);χ2=51.701, P=0.000]. The endometrial lesions rate in the menopause group was higher than that in the premenopause group [medicine-taking group: 69.70 ％ (46/66) vs. 92.98 ％ (106/114), χ2= 17.254, P= 0.000; non medicine-taking group: 46.15 ％ (35/65) vs. 63.53 ％(54/85), χ2 = 4.513, P= 0.034]. For the patients in the menopause group and the premenopause group, the incidence of endometrial lesions for those who took medicine for>5 years [96.00％(48/50), 85.19％(23/27)] was higher than that in the<2 years group and 2-5 years group [78.26％(18/23), 42.86％(6/14);95.12％(39/41), 72.00％(18/25) respectively], and there were statistical differences (χ2=7.619, P=0.022;χ2= 8.070, P= 0.018). The menopause was not correlated with staging, muscular lawyer infiltration and lymph metastasis postoperative (P> 0.05), but with the type of endometrial cancer (P= 0.013); the length of taking medicine was related with the type of endometrial cancer and the lymph metastasis (P=0.027). With the prolonged time of medicine-taking for postmenopause patients, the incidence of type Ⅱendometrial cancer and positive rate of lymph metastasis were also increased. Conclusions Taking TAM after surgery for breast cancer patients increases the risk of endometrial lesions. The longer the patients take the medicine, the greater risk of the lesions take, and the worse the pathological, histological type and prognosis of endometrial carcinoma are, which is more obvious for postmenopausal women who take TAM for more than 5 years.