Lactate dehydrogenase A (LDH-A) is a key enzyme during glycolysis, which increases the synthesis of related proteins and has elevated activity in cancer cells. The role of LDH-A in lung adenocarcinoma (LUAD) progression was investigated in the present study. Expression levels of LDH-A were assessed in LUAD samples, and the relationship between LDH-A expression status and the prognosis of LUAD patients was confirmed. The effect of LDH-A on proliferation, invasion, migration, and colony formation of cancer cells was assessed. We further determined the role of LDH-A in tumor growth in vivo by using xenograft LUAD tumor models. The potential mechanism of LDH-A promotion in LUAD progression was explored. LDH-A showed an abnormally high expression in LUAD, which is closely associated with poor prognosis in patients with LUAD. In in vitro experiments, silencing LDH-A expression in LUAD cells could effectively inhibit proliferation, invasion, migration, and colony formation of cancer cells. In in vivo experiments, tumor growth was markedly inhibited by LDH-A silencing in a xenograft model of LUAD. Notably, LDH-A could also promote tumor progression by regulating epithelial-mesenchymal transition (EMT)-related molecules. LDH-A can promote the malignant biological behaviors of LUAD cells, and thus can be a potential target for LUAD treatment.