ObjectiveTo investigate the expression of CD133 protein in primary lesions of gastric cancer and its clinical significance. MethodsThe expressions of CD133 protein in the primary lesion of tumor and normal gastric mucosa tissues confirmed by using histopathologic examination of 99 patients were detected by immunohistochemical staining. The correlation of CD133 protein expression with the clinicopathologic parameters and features after operation were analyzed. ResultsPositive cells of CD133 protein were localized in the gland parietal and cell membrane surface. The expression of CD133 protein in the cancer and normal gastric mucosa tissues were 29.29% (29/99) and zero, respectively (P=0.000). Expression of CD133 protein in tumor with diameter gt;5 cm was significantly higher than that in the tumor with diameter ≤5 cm (P=0.041). The expression of CD133 protein was correlated with TNM stage (P=0.044), lymph node metastasis (P=0.017), lymphatic vessel invasion (P=0.000), and vascular invasion (P=0.000). Logistic regression analysis revealed that invasion depth of tumor (P=0.011), lymph node metastasis (P=0.043), and TNM stage (P＝0.049) were independent risk factors for CD133 protein expression. Survival time of patients with positive expression of CD133 protein was significantly shorter than that negative expression of CD133 protein (P＝0.046). Cox proportial hazard regression model analysis demonstrated that lymph node metastasis (P=0.042), TNM stage (P=0.046), and positive expression of CD133 protein (P=0.046) were independent risk factors for patients survival. ConclusionThe CD133 protein expression in primary lesions is closely related with development, metastasis, and prognosis of gastric cancer.