Abstract: Objective To investigate the expression of microRNA-133（miR-133） in gastric cancer tissues and cell lines as well as its effect on apoptosis and invasion of gastric cancer cells. Methods The real-time quantitative PCR （qPCR） was used to detect the miR-133 level in 64 cases of gastric cancer tissues and corresponding adjacent normal tissues. Then， we analyzed the relationship between miR-133 expression and clinical pathological parameters（age， gender， tumor location， clinical stage， differentiation degree， invasion depth and lymph node metastasis）. The expression of miR-133 was detected in gastric cancer cell line AGS， SGC-7901， MKN-1， MKN-45， MGC-803， BGC-823 and GES-1， and the normal gastric mucosa cell line， GES-1， was used as the control. The gastric cancer cell with the lowest level of miR-133 was chosen for the transfection with the recombinant plasmid pCDNA3.1+miR-133. PI/Annexin V double staining and Transwell assay were used to detect the effect of miR-133 on apoptosis and invasion of cells. Results The relative expression of miR-133 in gastric carcinoma tissues was 0.347±0.024， lower than that of the adjacent tissues （P＜0.05）. Its expression was related to clinical stage， differentiation， depth of invasion and lymph node metastasis （P＜0.05）. Compared with the GES-1 cells， the miR-133 levels of gastric cancer cells were lower （P＜0.05）， and the expression level of MKN-45 was lowest. Compared with other two groups at 48 and 96 h after transfection， the apoptosis level was higher but the number of the cells was decreased in the overexpression group （P＜0.05）. Conclusion miR-133 was lowly expressed in gastric cancer tissues and cells， and upregulation of miR-133 can inhibit the invasion and apoptosis of gastric cancer cells.