<b><i>Background:</i></b> Accumulating evidence indicates that microRNAs play a key role in tumor progression and prognosis. However, the overall biological role and clinical significance of microRNA-552 (miR-552) in the pathogenesis of gastric cancer (GC) remain unclear. <b><i>Methods:</i></b> miR-552 expression was measured in 122 pairs of cancerous and noncancerous tissues and cell lines by quantitative real-time polymerase chain reaction. The relationship between miR-552 and the clinical parameters of patients was analyzed by the χ<sup>2</sup> test; Kaplan-Meier analysis and multivariate Cox regression analysis were used to predict the overall survival time and prognosis of patients with different expression of miR-552. Finally, CCK-8 and Transwell were used to detect the changes in cell proliferation, migration, and invasion ability. <b><i>Results:</i></b> miR-552 was expressed at markedly high levels in GC tissues compared to normal tissues and in some GC cell lines (<i>p</i> < 0.001). The upregulation of miR-552 was significantly associated with tumors with advanced TNM stage (<i>p</i> = 0.026), lymph node metastasis (<i>p</i> = 0.018), intestinal metaplasia (<i>p</i> = 0.044), and genomically stable subtype (<i>p</i> = 0.035). Moreover, GC patients with high miR-552 expression showed shorter overall survival (log-rank test, <i>p</i> = 0.011) than those with low expression. Meanwhile, miR-552 was an independent prognostic factor for GC patients (HR 5.657, 95% CI 1.619–19.761, <i>p</i> = 0.007). Finally, miR-552 overexpression promoted the proliferation, migration, and invasion of GC cells (<i>p</i> < 0.01). <b><i>Conclusion:</i></b> Taken together, our results indicate that miR-552, as an oncogene of GC, can promote cell proliferation, migration, and invasion, and miR-552 may be a novel prognostic biomarker for GC.