The levels of GAS5 and miR-21 were correlated with the clinicopathological characteristics of HCC. HCC patients with higher levels of GAS5 or with the lower levels of miR-21 have longer survival times. There are lower levels of GAS5 and higher levels of miR-21 in HCC cell lines (Be7402, SMMC-7721, and HCCLM3) than in normal liver L-02 cells, and the levels correlate with the aggression of the HCC cell lines. Knockdown of GAS5 upregulates miR-21 levels in Bel-7402 cells (weakly aggressive). Moreover, GAS5 that upregulated or downregulated the expression of PDCD4 and PTEN was reversed by inhibiting or overexpressing miR-21 level in Bel-7402 and HCCLM3 cells. Then, overexpression of GAS5 suppresses the migration and invasion of HCC cells and high expression of miR-21 largely eliminates GAS5-mediated suppression of HCC cell migration and invasion.