Abstract: Abstract: Objective To investigate the possible role of miR-449a/b in the occurrence of gastric cancer. Methods The expression of miR-449a/b and E2F1 mRNA in gastric cancer cells BGC-823 and gastric mucosal cells GES-1 were detected with qRT-PCR. miR-449a/b mimics or a negative control was transiently transfected into BGC-823 cells, and the changes in cell proliferation, apoptosis, and migration ability were assessed using CCK-8 assay, flow cytometry, and scratch wound healing assay, respectively. Western blotting was used to observe the effects of miR-449a/b upregulation on its target gene expression. The effects of transfection with an E2F1-over-expressing plasmid or an empty plasmid were analyzed on the expression level of miR-449a/b in BGC-823 cells using qRT-PCR and digital PCR. Results The gastric cancer cell line BGC-823 showed significantly a lowered expression of miR-449a/b compared with the normal gastric mucosal cell line GES-1 (P<0.01). Overexpression of miR-449a/b obviously inhibited the proliferation and migration and promoted apoptosis of BGC-823 cells (P<0.05). Overexpression E2F1 in the cells resulted in significantly up-regulated expression of miR-449a/b (P<0.001). Upregulation of miR-449a/b caused significant down-regulation of its direct target genes CDK4 and CDK6 and also of the expression of E2F1 protein via the CDKs-pRb-E2F1 signaling pathway. Conclusion The low expression of miR-449a/b and the high expression of E2F1 are both involved in the occurrence and progression of gastric cancer, and miR-449a/b negatively regulates E2F1 to inhibit the proliferation of gastric cancer cells.