Background and Purpose: Leiomyoma and leiomyosarcoma of uteri have similar clinical symptoms and overlapping imaging presentations but different prognoses. Preoperative diagnostics are essential. We aim to Investigate whether mass size in Magnetic resonance (MR) features can differentiate leiomyosarcoma (LMS) from atypical leiomyoma (ALM) and Typical Leiomyoma (LM). Methods: This retrospective study included 43 female patients with pathologically confirmed (LMS=2, ALM=23, LM=18) imaged with MRI before surgery. We evaluated the tumor volume with one-way ANOVA and post hoc Dunns multiple comparisons. Results: Typical leiomyoma was associated with a smaller size (diameter 5,4 cm volume 170 cm3)  and was significantly different from atypical leiomyoma (diameter 14,3 cm volume 1.032  cm3)  (P < 0.001). However, atypical leiomyoma is large and cannot be differentiated from leiomyosarcoma (diameter 13,1 cm volume 951 cm3). Conclusions: Mass size can be valuable for differentiating leiomyoma typical from atypical but not leiomyosarcoma from typical and atypical leiomyoma. Multiparametric analysis is required to determine atypical leiomyoma and leiomyosarcoma.