Objective: To investigate the feasibility and diagnostic accuracy of endometrial biopsy using Li Brush sampler in IUD users. Design: Clinical research Setting: A public teaching hospital in China. Population: IUD users with irregular uterine bleeding and IUD non-users who arranged for dilatation and curettage at the First Affiliated Hospital of Xi’an Jiaotong University, China from January 2018 to January 2020. Methods: This study was conducted in two parts. Part Ⅰ was to assess the impact of Li Brush on the position of IUDs. Transvaginal ultrasound was used to locate IUDs before and after sampling. Part Ⅱ was to explore the diagnostic accuracy of Li Brush in detecting endometrial lesions. Both IUD users and non-users were recruited, and the sampling satisfaction and accuracy of Li Brush were evaluated. Main outcome Measures: The positions of IUDs before and after sampling, cytopathological and histopathological diagnosis, sampling satisfaction rate. Results: Seventeen cases in part Ⅰ confirmed no significant difference in the position of IUDs before and after sampling (p=0.20). 112 IUD users and 139 IUD non-users were recruited in part Ⅱ. The Li Brush achieved 94.64% and 92.09% sampling satisfaction in the IUD group and control group, respectively, and the overall diagnostic accuracy was 88.04% and 93.33% in the two groups. Conclusions: Li Brush used for endometrial biopsy did not affect the position of IUDs and had high sampling satisfaction and accuracy for endometrial diagnoses.