The study aimed to investigate the roles of potassium voltage-gated channel subfamily D member 2 (KCND2) in lung adenocarcinoma (AD). RNA sequencing data from The Cancer Genome Atlas (TCGA) database showed that the expression of KCND2 was elevated in lung AD samples compared to the normal samples, and its upregulation was significantly associated with the unfavorable clinic outcome of lung AD patients. Cell proliferation and transwell assays revealed that the growth, migration, and invasion of lung AD cells, which was crucial to cancer aggressiveness, were markedly inhibited after the depletion of KCND2. Importantly, we demonstrated that the depletion of KCND2 suppressed the biological behaviors of lung AD cells via restraining the expression of four tumor-related genes including PCNA, CDH2, SNAI1, and MMP2. Overall, KCND2 promotes the aggressiveness of lung AD and can be considered as a potential predictor of the prognosis of lung AD patients. Downregulation of KCND2 may contribute to the therapy of lung AD.