Objective To explore the value of active surveillance (AS) for papillary thyroid microcarcinoma (PTMC) tumor growth with ultrasound.Methods A retrospective collection of 196 patients who underwent ultrasound-guided fine-needle aspiration biopsy at West China Hospital of Sichuan University from January 2014 to December 2018 were pathologically diagnosed as PTMC, and no cervical lymph node metastasis was found on ultrasound, and AS was performed. According to the change of the maximum diameter of the nodule, the patients divided into the largest diameter increase group, the largest diameter stable group and the largest diameter reduction group. According to the nodule volume change, the patients divided into the volume increase group, the volume stable group and the volume reduction group. The differences in the patient’s gender, age, with Hashimoto’s thyroiditis, follow-up time, tumor size, boundary, shape, echo, aspect ratio, calcifications, multifocality, bilateral involvement, other nodule, surrounding tissues and cervical lymph nodes between the different groups were analyzed. In order to clarify the related factors of tumor growth.Results One hundred and ninety six patients had ultrasound AS time ranging from 6 to 79 months, with the median (quartile) time were 16.0 (10.0, 30.0) months. One hundred and seventeen patients (59.7%) were in AS for 6 to 63 months, with the median (quartile) time were 13.0. (8.0, 22.0), surgical treatment were performed after termination of AS. Forty-five patients (23.0%) continued to perform AS, 34 patients (17.3%) did not continue to perform AS in our department. There were no significant reduction in the maximum diameter and volume of the nodules in all cases. Among them, 9 cases (4.6%) had an increase in the maximum diameter of the nodules, and 187 cases (95.4%) had a stable maximum diameter. Forty cases (20.4%) had an increase in the volume of the nodules, and 156 cases (79.6%) had a stable volume of the nodules. Compared of the maximum diameter change of nodules between the two groups, there was a significant difference in the age of patients (P<0.05). Compared of the maximum volume change between the two groups, there were significant differences in age, follow-up time and initial nodule volume (P<0.05). Logistic regression analysis showed that younger age was an independent risk factor for PTMC nodule enlargement [OR＝0.956, 95%CI (0.921, 0.991), P＝0.015].Conclusions Younger age is a risk factor for PTMC tumor growth. We should adopt a more active monitoring program for younger patients. The increase of PTMC tumor volume can be more easily monitored than the increase of its maximum diameter, so it can be used as an indicator to predict nodule growth at an earlier stage in AS.