Abstract: 【Abstract】 Objective To detect the expression of octamer-binding protein-4（OCT4）in gastric cancer cell lines with different differentiation (MKN-28, SGC-7901, BGC-823) and normal gastric mucosal cells line GES-1, and further assess the relationship between OCT4 expression and the differentiation grade of gastric carcinoma cells. Methods Expression level of OCT4 in GES-1, MKN-28, SGC-7901 and BGC-823 was detected by reverse transcription-polymerase chain reaction (RT-PCR), and OCT4 siRNA was employed to interfere OCT4 expression in BGC-823 cell lines. Detect the quantity of OCT4 mRNA and OCT4 protein by fluorescent quantitative PCR and Western blot respectively. In addition, the invasion ability was analyzed via Transwell chamber. Results The normal gastric mucosal cells did not express OCT4 and there was higher expression of OCT4 in gastric cancer cell lines with poorly differentiation (P<0.05). The expression of OCT4 in BGC-823 cells was the highest. The expression of OCT4 mRNA and OCT4 protein were decreased distinctly in BGC-823 cells after being interfered by OCT4 siRNA (P<0.05). After being interfered by OCT4, BGC-823 cells were less aggressive, and the number of penetrating cells was decreased (P<0.05). Conclusion The OCT4 expression level is associated with gastric cancer differentiation. OCT4 may play an important role in the differentiation and invasion of gastric cancer cell and it may serve as a reference index in predicting the malignant grade of gastric cancer.