Abstract: Objective To explore the application value of Bosniak classification system in CT diagnosis of renal cystic lesions, and summarize CT features according to the item specifics. Methods A total of 39 cystic renal masses of 38 patients underwent surgical treatment and were confirmed by histopathological examination in our hospital. The multislice CT (MSCT) features of cystic masses such as the size of the capsule, the thickness of the capsule wall, the quantity and thickness of the separation, the reinforcement of the separation, calcification, solid components and their enhancement were used for Bosniak classification, and compared with the histopathological results. Results Among the 39 lesions, 10 were classified as Bosniak Ⅰ (benign by histopathological examination); 6 as Bosniak Ⅱ and IIF (benign by histopathological examination); 6 as Bosniak Ⅲ (3 lesions were malignant by histopathological examination, including 2 cases of clear cell carcinoma and 1 case of mucinous tubular and spindle cell carcinoma, with a malignancy rate of 50%); 11 as Bosniak Ⅳ (10 lesions were malignant by histopathological examination, with a malignancy rate of 91%). Conclusion The Bosniak classification system has high application value in diagnosing cystic renal masses with MSCT, which can provide meaningful reference value in clinical diagnosis and treatment. The rate of malignancy will increase with Bosniak classification, especially for Ⅰ and Ⅳ. But the items of level Ⅱ, ⅡF and Ⅲ are tedious, the diagnostic criteria are intersecting, and the observer's subjectivity has a great influence on it. We need to observe the fine structure of the capsule carefully use thin scanning when we make the diagnosis. For lesions that cannot be accurately classified, they should be classified into higher categories, followed up closely or punctured biopsy if necessary.