Abstract: ob＜x＞jective: To study the effects of long-chain noncoding RNA AC138128.1 (lncRNA AC138128.1) on the proliferation and apoptosis of gastric cancer cells and the role of microRNA-9 (miR-9). Methods: gastric cancer cell lines overexpressing lncRNA AC138128.1 and/or miR-9 were constructed by plasmid transfection. The ex＜x＞pression levels of lncRNA AC138128.1 and miR-9 were verified by qRT-PCR. The cell proliferation ability was detected by CCK8 assay, and the apoptosis level was detected by TUNEL assay. The tumorigenicity of gastric cancer cells in vivo was evaluated by nude mouse experiment. Results: lncRNA AC138128.1 was low expressed in gastric cancer cell line; Up regulation of lncRNA AC138128.1 can significantly inhibited the proliferation and promoted apoptosis of gastric cancer cell line. In vivo, up regulation of lncRNA AC138128.1 could effectively reduce the tumorigenicity of gastric cancer cells. Up regulation of miR-9 could significantly reverse the effects of lncRNA AC138128.1 on the proliferation and apoptosis of gastric cancer cells. Conclusion: lncRNA AC138128.1 may inhibit the proliferation and promote apoptosis of gastric cancer cells by regulating miR-9, suggesting that lncRNA AC138128.1 may play a positive role in the treatment of gastric cancer