The signal transducer and activator of transcription-5 (STAT5) protein has been shown to play an important role in tumor progression through stimulating cell proliferation and preventing apoptosis. STAT5 activation has been observed in a variety of human tumors and cancer cell lines. However, it is not clear how activated STAT5 is expressed in colon cancer. In this study, we aimed to investigate phospho-STAT5 (activated form of STAT5) expression and its relationship with the clinicopathological factors and overall survival of patients with colonic adenocarcinoma. A total of 121 histological samples were selected for this study. Immunohistochemistry was used to detect the expression of phospho-STAT5. Analysis of the immunohistochemical staining was based on the proportion of stained cells in the field: positive, >15% stained cells, and negative, <15% stained cells. Survival times were analyzed using the Kaplan-Meier method, and the differences between groups were assessed with the log-rank test. A multivariate Cox regression model was used for prognostic power analysis. Expression of phospho-STAT5 was observed in the cytoplasms of colonic adenocarcinoma cells. Univariate analysis showed that phospho-STAT5 immunoreactivity was correlated with the depth of tumor invasion (P-value = 0.009), tumor-node-metastasis (TNM) stage (P-value = 0.048) and shorter overall survival times (P-value = 0.026). Lymph node metastasis, distant metastasis and TNM stage were associated with shorter overall survival times (P-value range from 0.003- < 0.001). Multivariate analysis showed that only distant metastasis was an independent predictor of overall survival time (P-value = 0.016). Our findings first demonstrate that phospho-STAT5 is frequently present and active in colonic adenocarcinoma and related to poor prognosis.