LncRNA SNHG14 was markedly up-regulated in gastric cancer tissues and cells. Knockdown of SNHG14 significantly inhibited SGC-7901 cell viability, migration, invasion, and promoted cell apoptosis.In addition, miR-145 was negatively regulated by SNHG14 and the effects of SNHG14 knockdown on cell viability, apoptosis, migration, invasion, and the expression of apoptosis-related proteins and EMT-markers were reversed by inhibition of miR-145 at the same time. Furthermore, SOX9 was verified as a functional target of miR-145, and miR-145 regulated tumor malignant behaviors through regulating SOX9. Besides, knockdown of SNHG14 inhibited the expression of p-PI3K, p-AKT, and p-mTOR and promoted PTEN expression, where miR-145 inhibition had opposite effects. Moreover, the activated PI3K/AKT/mTOR pathway caused by miR-145 inhibition was counteracted after knockdown of SOX9.