BACKGROUND Ovarian clear cell carcinoma (CCC) is regarded as grade 3 tumor, and the National Comprehensive Cancer Network (NCCN) Clinical Practice Guidelines recommend adjuvant chemotherapy for the tumor even at stage IA. However, CCC often showed chemo-resistant phenotype, and the effect of adjuvant chemotherapy still remained uncertain. METHODS Clear cell carcinoma cases treated at collaborating institutions during the period 1992-2005 were retrospectively identified. After a central pathological review, survival analysis was estimated by the Kaplan-Meier method, and prognostic factors were evaluated using a Cox regression model. RESULTS Among 219 patients with stage I CCC, 195 patients received adjuvant chemotherapy (C+) and 24 patients (C-) did not. The C+ group had 77 pT1a and 118 pT1c cases, and the C- group included 18 pT1a and 6 pT1c tumors (P < 0.001). The median age was 52 years in the C+ group and 57 years in C- group (P = 0.04). During the median follow-up period of 48 months (range, 7-160 years), relapse was observed in one patient (4%) in the C- group and in 35 patients (18%) in the C+ group. There were no statistical differences of progression-free survival and overall survival between the C+ and the C- groups. Multivariate analysis revealed that peritoneal cytology status (P = 0.02) and pT status (P = 0.04) were independent prognostic factors for progression-free survival; however, adjuvant chemotherapy was not a prognostic factor (P = 0.80). CONCLUSIONS Although the present study was a limited retrospective investigation, it suggested that adjuvant chemotherapy had little impact on the survival of stage I CCC patients. Further strategy, such as a molecular targeting agent, is needed to improve survival of CCC, especially in cases with positive peritoneal washing.