Background: Benign leiomyomas (LM) and malignant leiomyosarcomas (LMS) can be distinguished by increased cellularity with mitotic activity. Uterine smooth muscle tumors of uncertain malignant potential (STUMP) are a group of rare tumors in between, for which there is still no standardized classification, nor any definitive preoperative imaging or laboratory investigations regarding the possible inclusion of STUMP in the differential diagnosis. Methods: In this study, we retrospectively reviewed 6 cases of STUMP, and assessed their pathogenesis, risk factors, and prognostic features. Results: The mean age of STUMP patients was 40.6 years old. No recurrence has been reported in all six cases after more than 3.6 years of follow-up. The mean tumor size was 9.44 cm (range 6.14–12.21). 4 cases (66.7%) with 5 mitoses, 1 case (16.7%) with 5–9 mitoses, and 1 case (16.7%) with >10 mitoses per 10 high-power fields. Immunohistochemical staining for cyclin dependent kinase nhibitor 2A (p16), tumor protein p53 (p53), and Antigen KI-67 (Ki-67) was 100% positive (2/2, 6/6, and 6/6, respectively). The estrogen receptor (ER) expression rate was 50.0% (3/6), and the progesterone receptor (PR) was 33.3% (1/3). There was no correlation between the expression of these biomarkers and mitotic counts or recurrence. Conclusions: The current immunohistochemical biomarkers are ineffective in determining the probability of malignancy in STUMP patients with desire of further fertility. Detection of gene expression profiles or variants using next-generation molecular techniques may aid in disease prediction, diagnosis, treatment, and prognosis.