Objective: To investigate the expression of miR-520a in gastric cancer and its effect on the biological function in gastric cancer cells. Methods: The expression of miR-520a in gastric tissues and gastric cells was detected by real-time PCR. Lentivirus was used to over-express miR-520a in gastric cancer SGC7901 cells, and the effect of miR-520a on proliferation, apoptosis, invasion and migration of gastric cancer cells and the sensitivity to cisplatin (DDP) was evaluated in vitro. In addition, the effect of miR-520a over-expression on the growth of xenograft tumor was observed in vivo. Results: The expression of miR-520a in gastric cancer tissues was significantly lower than that in the adjacent normal tissues. Compared with normal gastric mucosal epithelial GES-1 cells, the expression of miR-520a was significantly decreased in gastric cancer SGC7901 cells and even lower in cisplatin resistant SGC7901/DDP cells. MiR-520a over-expression promoted apoptosis and inhibited cell proliferation, invasion and migration in SGC7901 cells. MiR-520a over-expression promoted the drug sensitivity of SGC7901 cells to DDP. Xenograft tumor experiment data showed that the miR-520a over-expression slowed down the tumor growth in nude mice. Conclusion: MiR-520a can inhibit the occurrence and development of gastric cancer and enhance the sensitivity of gastric cancer cells to cisplatin.