Accumulating evidence has shown that microRNAs are involved in cancer development and progression.However, it remains unknown about the potential role of miR-19a in the pathogenesis of gastric cancer. Here, wereport that suppressor of cytokine signaling 1 (SOCS1) is a novel target of miR-19a in gastric cancer cells andthat miR-19a expression is inversely correlated with SOCS1 expression in gastric cancer cells and a subset ofgastric cancer tissues. Ectopic expression of miR-19a dramatically promoted proliferation and tumorigenicity ofgastric cancer cells both in vitro and in vivo. Moreover, we showed that silencing of SOCS1 promoted cell growthand colony formation resembling that of miR-19a overexpression, whereas re-introduction of SOCS1 (withoutthe 3’-UTR) attenuated the pro-tumorigenic functions. Taken together, our findings suggest that the SOCS1gene is a direct target of miR-19a, which functions as an oncogenic miRNA in gastric cancer by repressing theexpression of tumor suppressor SOCS1.