Abstract： Objective:To explore the consistency of MRI-based ovarian-adnexal report and data system (O-RADS) score and its diagnostic value for ovarian adnexal masses.Methods:The MRI data of 309 patients with ovarian adnexal masses confirmed by pathology were retrospectively collected from January 2017 to August 2021 in the Second Affiliated Hospital of Soochow University, including 327 lesions consisted of 250 benign lesions, 21 borderline lesions, and 56 malignant lesions confirmed by pathology. Borderline and malignant lesions were classified into the malignant group ( n=77) and benign lesions were classified as benign group ( n=250). Two radiologists scored all lesions according to the MRI-based O-RADS, and scored again after 6 months. The proportion of borderline/malignant lesions in each MRI-based O-RADS score was calculated. The weighted Kappa test was used to assess the intra-reader and inter-reader consistency of the image interpretation results. The receiver operating characteristic (ROC) curve analysis was used to evaluate the diagnostic efficacy of MRI-based O-RADS classification for distinguishing benign and malignant ovarian adnexal masses. Results:The weighted Kappa value of the MRI-based O-RADS score between the two radiologists was 0.810 (95%CI 0.764-0.855), and the weighted Kappa values of the two radiologists′ scores at different times were 0.848 (95%CI 0.806-0.889) and 0.875 (95%CI 0.835-0.914), respectively. The borderline/malignant lesions accounted for 0/16, 0.8% (1/127), 10.1% (10/99), 76.0% (57/75), 9/10 and 0/17, 0 (0/122), 8.0% (8/100), 76.2% (48/63), and 84.0% (21/25) of the lesions in the two radiologists based on the MRI O-RADS score of 1, 2, 3, 4, and 5, respectively. When adopting O-RADS score>3 as a cut-off value, the area under the ROC curve of the two radiologists for distinguishing benign and malignant ovarian adnexal masses was 0.928 (95%CI 0.895-0.954) and 0.942 (95%CI 0.911-0.965), respectively. The sensitivity was 0.857 and 0.896, the specificity was 0.924 and 0.924, and the accuracy was 0.908 and 0.917 respectively.Conclusion:The MRI-based O-RADS yields high diagnostic efficiency in the evaluation of benign and malignant ovarian adnexal masses, and the intra-reader and inter-reader consistency of the image interpretation is strong.