Objective: To analyze the characteristics of growing Breast Imaging Reporting and Data System (BI-RADS) category 3 lesions and malignant tumors during breast ultrasound follow-up. Methods: From November 2018 to November 2021, 115 patients with growing BI-RADS 3 lesions were followed up. The patients were diagnosed and followed up with breast ultrasound. Changes in growing BI-RADS 3 lesions, the correlation between the changes and ultrasound findings, the influencing factors of malignant growing BI-RADS 3 lesions, and the predictive value of ultrasound findings for condition changes were analyzed. Results: At the end of follow-up, there were 91 cases of benign lesions and 24 cases of malignant lesions. The ultrasound findings such as the growth rate of the maximum diameter, the growth rate of anterior-posterior diameter, boundary and internal echo showed no statistically significant difference between benign and malignant lesions (P<0.05). Multivariate logistic regression analysis showed that the growth rate of the maximum diameter, the growth rate of anterior-posterior diameter, and boundary were influencing factors for malignant growing BI-RADS3 lesions (P<0.05). The receiver operating characteristic curve showed that the areas under the curve (AUC) of the growth rate of the maximum diameter, the growth rate of anterior-posterior diameter, and boundary to diagnose benign and malignant growing BI-RADS 3 lesions were 0.635, 0.820, and 0.598, respectively. The AUC of the three in combination was 0.868. Conclusion: Changes in growing BI-RADS 3 lesions are closely related to ultrasound findings, which indicates that ultrasound findings can help to predict the changes in BI-RADS 3 lesions.