Abstract: Objective STAT5 activation(Phospho-STAT5,P-STAT5)has been observed in a variety of human tumors.Many studies have found that poor prognosis is associated with the expression of phospho-STAT5.However,it is not clear how activated STAT5 is expressed in colon cancer.In this study,we aimed to investigate phospho-STAT5 expression and its relationship with clinicopathological factors and overall survival in Stage Ⅱ colonic adenocarcinoma.Methods 122 histological samples of Stage Ⅱ colonic adenocarcinoma were selected for this study.Immunohistochemistry was used to detect the expression of phospho-STAT5.Results Phospho-STAT5 expression was observed in the cytoplasm of colonic adenocarcinoma cells.A significant relationship was found between phospho-STAT5 expression and tumour differentiation(P=0.033).Univariate analysis showed that shorter overall survival was correlated with phospho-STAT5 immunoreactivity(P=0.047,log-rank test).Multivariate analysis showed that phospho-STAT5 was not an independent predictor in relation with shorter overall survival(P=0.053,hazard ratio=2.41).Conclusion Expression of phospho-STAT5 is correlated with shorter survival in patients with Stage Ⅱ colonic adenocarcinoma.It may be of great value in evaluating the expression of phospho-STAT5 for adjuvant systemic therapy in surgically treated patients with Stage Ⅱ colonic adenocarcinoma.