Background: Gastric cancer is a worldwide cancer with poor prognosis. Identification of diagnostic biomarkers and effective therapeutic targets is important in the treatment and diagnosis of gastric cancer. Recently, researchers have found that microRNAs play several important roles in carcinogenesis. The purpose of this study was to investigate the relationships between miR-421 expression patterns in human gastric cancer tissues with clinicopathological features. Methods: Sixty gastric carcinoma and 18 non-tumor tissues were collected from the Secondary Hospital of Ningbo, China. For quantitative detection of the expression level of miR-421, total RNA was extracted and then reverse transcription-polymerase chain reaction was performed. The relationship between miR-421 expression in gastric cancer and clinicopathological features was analyzed. After miR-421 inhibitor was transfected into gastric cancer cells, cell growth was measured by MTT assay. Finally, the expression of its target genes was detected by Western blotting. Results: The miR-421 was over-expressed in 73.33% (44/60) of the gastric cancer samples examined. Over-expression of miR-421 in gastric cancer tissues was not found associated with clinicopathological features. The positive detection rate of miR-421 was higher than that of serum carcino-embryonic antigen (χ2 = 39.811, P < 0.001). Inhibition of miR-421 expression decreased the growth of both MGC-803 and SGC-7901 gastric cancer cells in vitro, with up-regulating the expression of its cancer-related target genes, CBX7 and RBMXL1. Conclusions: miR-421 may involve in the early stage of stomach carcinogenesis and could be used as an efficient diagnostic biomarker. © 2009 Springer.