B-cell translocation gene 3 (BTG3) is a member of the BTG family which inhibits cell proliferation, metastasis, and angiogenesis, and also regulates cell-cycle progression and differentiation in a variety of cell types. However, there is no study to analyze BTG3 expression in epithelial ovarian carcinoma (EOC). Here, we investigated the expression of BTG3 in EOC carcinogenesis and subsequent progression. BTG3 mRNA expression was detected by real-time RT-PCR in ovarian benign and malignant tumors. The expression of BTG3 protein was examined by immunohistochemistry on tissue microarrays containing ovarian normal tissue, benign and borderline epithelial ovarian tumors, and EOCs. Relationships of BTG3 with both EOC clinicopathology and prognosis were analyzed statistically. The expression of BTG3 protein was also evaluated in ovarian normal tissue, benign tumors, and EOCs by western blot. The BTG3 mRNA expression level was higher in ovarian normal tissue and benign tumors than that in borderline, primary, and metastatic carcinoma (p < 0.05), and was negatively correlated with dedifferentiation and FIGO staging of EOC (p < 0.05). Using western blot, BTG3 protein was found lower in EOCs compared to the normal and benign tumors (p < 0.05), and poorly differentiated EOCs showed lower BTG3 expression than well-differentiated and moderately differentiated EOCs (p < 0.05). Immunohistochemically, BTG3 protein expression was statistically lower in EOCs than normal tissue and benign tumors (p < 0.05). EOC patients with low BTG3 protein expression showed a higher incidence of metastasis (p = 0.020), poor differentiation (p = 0.030), and shorter disease-free time and overall survival time (p < 0.05). By using Cox's proportional hazard model, BTG3 protein expression and FIGO staging were independent prognostic factors for both disease-free time and overall survival time of EOCs (p < 0.05). It was suggested that down-regulated BTG3 expression might play roles in the pathogenesis and aggressiveness of EOC. BTG3 protein expression may be considered as a good marker to indicate the favorable prognosis of EOCs.