Purpose of investigation: To compare low-grade serous ovarian carcinomas (LGSC) and high-grade serous ovarian carcinomas (HGSC). Materials and Methods: Between 1985 and 2013, patients with LGSC and HGSC were identified through pathological review using the 2014 World Health Organization classification. The clinical outcome of patients with LGSC and HGSC was retrospectively compared. Results: A total of 174 cases, 5 (2.9%) cases of LGSC and 169 (97.1%) cases of HGSC (97.1%) were identifies for our study. The proportion of patients who underwent optimal surgery was higher for LGSC than HGSC (p = 0.03). We found no other statistically significant differences in the characteristics of the two groups. Survival analysis revealed that the histological subtype was not an independent prognostic factor of Progression-free survival (p = 0.28) or overall survival (p = 0.43). Conclusions: LGSCs may be a rare histological subtype in Japan and may not be associated with a different prognosis than HGSC. Larger scales studies are needed to examine the clinical significance of LGSC.