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Human DEAD‐box RNA helicase gene DDX6 was cloned from B‐cell lymphoma cell line RC‐K8. Previously, we reported that DDX6 acts as oncogene in several cancers such as colorectal cancer and hepatocellular carcinoma. However, the detailed mechanism of DDX6 action in carcinogenesis is largely unknown. In this study, we examined the functions of DDX6 in clinical gastric cancer (GC) samples and GC cells. DDX6 protein expression levels of cancer samples were higher than those of the adjacent normal tissues in 25 clinical GC samples (median value: 1.4 times higher). Also, the results of an RNA immunoprecipitation‐assay (RIP‐assay) showed that DDX6 associated with c‐Myc mRNA. Moreover, enforced overexpression of DDX6 promoted both mRNA and protein expression of c‐Myc in GC cells. On the other hand, the gene silencing of DDX6 induced growth suppression through down‐regulation of c‐Myc in GC cells grown in either two or three dimensions. Furthermore, c‐Myc mRNA expression levels of cancer samples were higher than those of the adjacent normal tissues in DDX6 up‐regulated‐GC clinical samples. Our findings in this study suggested that DDX6 acted as oncogene in GC cells through promotion of c‐Myc expression by association with the mRNA of c‐Myc.