AIM: To investigate the expressions of signal transducer and activator of transcription 3 (Stat3) and tyrosine-activated Stat3 (p-Stat3) in epithelial ovarian carcinoma (EOC) and their relationships with clinical pathological parameters or prognosis. METHODS: Immunohistochemical methods were used to detect the expressions of Stat3 and p-Stat3 in EOC, benign ovarian tumors and normal ovarian tissues, after which an analysis of results with clinical pathological or prognosis was given. RESULTS: The expressions of Stat3 and p-Stat3 in EOC were significantly higher than in normal ovarian epithelial tissues or benign ovarian tumor tissues (P < 0.0125) and the expression of Stat3 protein was highly correlated with the expression of p-Stat3 protein (P < 0.01). The positive rate of Stat3 in stages of III and IV (96.9%) was significantly higher than in stages of I and II (72.2%) (P < 0.05). Meanwhile, p-Stat3 expression was significantly correlated with disease stage, degree of differentiation and lymph node metastasis. Along with higher clinical stage (P < 0.05), p-Stat3 expression was gradually increased. The p-Stat3 expression was negatively correlated with the prognosis of EOC patients (P < 0.01). CONCLUSION: Overexpression and overactivation of Stat3 was found in EOC tissues, and the constitutive activation of Stat3 signaling pathway may play an important role in the invasion and prognosis of EOC.