AIM: To assess whether the molecular markers of malignant tumors could improve the understanding of tumor characteristics, and to observe the characteristics of expression of cell cycle markers Ki-67 and cyclin A in esophageal carcinoma and to analyze the relationship between proliferative activity of cancer cells and clinicopathological factors. METHODS: Seventy of surgically resected esophageal squamous cell carcinoma (SCC) were examined by immun-ohistochemistry utilizing commercially available antibodies. Nuclear staining was regarded as a positive result. At least 50 fields in each tumor and non-tumor section were evaluated at a medium power (×200) to determine the proportion of tumor cells and the staining intensity of nuclei in the entire sections. RESULTS: Ki-67 and cyclin A were only expressed in base cells of normal esophageal mucosa. The positive immuno-staining of nuclei of SCC was significantly higher than that in normal esophageal mucosa (t = 13.32 and t = 7.52, respectively, P<0.01). The distribution of positively stained was more diffuse and stronger in poorly differentiated SCC. Both Ki-67 and cyclin A expressions were related to histological grades of tumors (t = 3.5675 and t = 3.916; t = 2.13, respectively, P<0.05) but not to the sex and age of the patients, tumor size, lymphatic invasion, location, or stage grouping. CONCLUSION: The proliferative activity of cancer cells may be understood by immunohistochemistry of Ki-67 and cyclin A in Chinese patients with esophageal SCC. These cell cycle markers may serve as an indicator of cancer cell proliferation rate. The overexpression of cell cycle markers Ki-67 and cyclin A suggests the poor SCC differentiation in patients with esophageal carcinoma. AIM: To assess whether the molecular markers of malignant tumors could improve the understanding of tumor characteristics, and to observe the characteristics of expression of cell cycle markers Ki-67 and cyclin A in esophageal carcinoma and to analyze the relationship between proliferative activity of cancer cells METHODS: Seventy of surgically resected esophageal squamous cell carcinoma (SCC) were examined by immuno- ohistochemistry used commercially available antibodies. Nuclear staining was viewed as a positive result. At least 50 fields in each tumor and non-tumor section were RESULTS: Ki-67 and cyclin A were only expressed in base cells of normal esophageal mucosa. The positive immuno- staining of nuclei of SCC was significantly higher than that in normal esophageal mucosa (t = 13.32 and t = 7.52, respectiv The distribution of positively stained was more diffuse and stronger in poorly differentiated SCC. Both Ki-67 and cyclin A expressions were related to histological grades of tumors (t = 3.5675 and t = 3.916; t = 2.13, respectively, P <0.05) but not to the sex and age of the patients, tumor size, lymphatic invasion, location, or stage grouping. CONCLUSION: The proliferative activity of cancer cells may be appreciated by immunohistochemistry of Ki-67 and cyclin A in Chinese patients with esophageal SCC. These cell cycle markers may serve as an indicator of cancer cell proliferation rate. The overexpression of cell cycle markers Ki-67 and cyclin A suggests the poor SCC differentiation in patients with esophageal carcinoma.