ObjectiveTo assessment the value of strain ratio(SR) in differentiating benign and malignant breast lesions of BI-RADS Ⅳ diagnosed by conventional ultrasound.MethodsElastosonography was performed on 64 patients with breast lesions of BI-RADS Ⅳ diagnosed by conventional ultrasound.SR (strainnormal neighboring tissues /strainbreast lesion) was calculated by the software equipped with the ultrasonic machine.Pathology of the lesions after biopsy or operation was considered as standard,SRs of benign and malignant breast lesions were compared with independent-samples t test.The diagnostic value of SR was evaluated by receiver operating characteristic (ROC) curve analysis.Results SRs of 34 benign breast lesions and 30 malignant breast lesions were 2.85 ± 1.30 and 5.03 ± 2.50 respectively,there was significant difference between them( t =- 4.29,P =0.000).Area under the curve of diagnosing benign and malignant of breast lesions was 0.875 for SR( P ＜0.0001).If the cut-off point of SR was 3.26,the sensitivity in differentiating breast lesions was 83.33％,while the specificity was 82.35％.Conclusions SR is a helpful elasticity parameter for differentiating benign and malignant breast lesions of BI-RADS Ⅳ diagnosed by conventional ultrasound.