We report a rare case of ovarian leiomyoma with extensive edema in a 55-year-old woman. Magnetic resonance (MR) imaging revealed an ovarian mass with distinct portions of predominantly low intensity and predominantly high intensity on T2-weighted image. The portion with low signal showed weak enhancement on contrast study, and the portion with high intensity suggested extensive edema of fibrous stroma. Furthermore, the mass showed low signal intensity similar to that of the myometrium on diffusion-weighted image and yielded high values on apparent diffusion coefficient (ADC) map image. Extensive edema of ovarian leiomyoma shows unusual MR imaging findings that require careful interpretation.