Abstract: Objective According to previous studies, overactivation of the MAPK (mitogen-activated protein kinase) pathway plays an important role in driving the progression of cancer and is correlated with the poor prognosis of colon cancer.However, there are few studies focusing on the effect of this overactivation of the MAPK pathway in different stages of tumor devel-opment.To specify the role of p-ERK in locally advanced colon cancer, we investigate the clinical significance of p-ERK1/2 in colon carcinomas of stage IIIB. Methods: Data from 56 patients with colon carcinoma seen in our hospital be-tween 1997 and 2002 were collected.We analyzed the carcinoma tissues and the corresponding adjacent mucosa.Phos-phorylation of ERK1/2 was detected in the tissue sections with immunohistochemistry.We used SPSS statistical analysis software to analyze the relationship among phosphorylation of ERK1/2, clinicopathologic characteristics, age, gender, tumor location, differentiation, and 5-year survival rate. Results: p-ERK1/2 was located in the cytoplasm and/or nucleus.p-ERK1/2 was almost absent in the tissues adjacent to colon cancer.Compared with normal mucosa, 26 (46.4%) carcinoma tissues showed a higher level of phosphorylation of ERK1/2, 29 (51.8%) carcinoma tissues showed no difference, and only one case (1.7%) showed a lower phosphorylation level.The expression of p-ERK1/2 was not related to age, gender, tumor location or differentiation.Patients with higher phosphorylation levels of ERK1/2 showed a longer 5-year survival rate.Age, gender, differentiation and location were not correlated with survival. Conclusion: The MAPK pathway may not play the most important role in controlling the biological behavior of locally advanced colon carcinoma.