Objective Gastric cancer is a genetically heterogeneous disease that progresses via different oncogenes. MicroRNA (miRNA) can regulate oncogene expression at the post-translational level. In this review, we summarize the most commonly altered miRNAs and their possible roles in cancer initiation and progression in gastric cancer. Data sources Most articles were identified by searching PubMed online resources using the key terms of microRNA and gastric cancer. Study selection Mainly original milestone articles and critical reviews written by major pioneer investigators in the field were selected, and the 69 most important articles were cited finally. Results A set of miRNAs are consistently deregulated in gastric cancer, although there is no clear miRNA expression profiles, such as miR-21 and miR-17 (similar to 92 clusters). These deregulated miRNAs play important roles in promoting cell proliferation, tumor metastasis, and chemotherapeutic resistance in gastric cancer by targeting different oncogenes. Clinical relevance of these deregulated miRNAs is proved to be associated with TNM stages, metastasis, and prognosis of gastric cancer patients. In addition, circulating miRNAs are promising noninvasive biomarkers for gastric cancer. Conclusions miRNAs have produced a novel paradigm in research in gastric cancer. These small molecules play macroroles in gastric cancer initiation and progression. These results will help us improve management of gastric cancer in future.