MicroRNAs (miRNAs) may function as oncogenes or tumor suppressors. Here, we show that miR-27a is up-regulated in human gastric adenocarcinoma. Suppression of miR-27a inhibits gastric cancer cell growth. Subsequently, prohibitin is identified as a potential miR-27a target, combining bioinformatics and microarray analysis. EGFP report experiment also confirms that the 3' untranslated region (3'UTR) of prohibitin carries the directly binding site of miR-27a. After knockdown of miR-27a in gastric cancer cells, mRNA level and protein level of prohibitin are both elevated. Down-regulation of prohibitin by miR-27a may explain why suppression of miR-27a can inhibit gastric cancer cell growth, further supporting that miR-27a functions as an oncogene.