The prognostic nutritional index (PNI), which reflects preoperative malnutrition, is useful for predicting the incidence of postoperative complications and has been reported in recent years to predict the long-term prognosis of various malignancies. The purpose of this study was to clarify the significance of PNI as a prognostic factor for early-stage clear cell ovarian carcinoma. A total of 82 patients with stage I-II (FIGO 2014) ovarian clear cell carcinoma undergoing primary surgery at our hospital from January 2005 to December 2017 were enrolled. PNI was calculated using the formula: 10 × serum albumin (g/ dL) + 0.005 × peripheral blood lymphocyte count (/mm3). Preoperative PNI exhibited relatively high area under the curve value (0.709) for 5 year survival, and the optimal cutoff value was 46.5. The overall survival was significantly shorter in the PNI-low group than in the PNI-high group. Multivariate analysis showed that high PNI was a significant independent prognostic factor for favorable prognosis (hazard ratio = 0.102, p = 0.010). There was no significant difference in recurrence-free survival between the two groups (p = 0.220), but the postrecurrence survival was significantly longer in the PNI-high group than in the PNI-low group (p = 0.0383). The preoperative PNI was a useful predictor of prognosis, even in early-stage ovarian clear cell carcinoma.