Polypeptide N-acetyl-galactosaminyltransferases (GALNTs) regulate several biological processes and thus, dysregulation of GALNTs' functions often leads to various diseases. Recent studies have suggested both tumor-suppressive and promoting roles of GALNTs in various cancer types. However, the roles of GALNTs in lung cancer progression and the underlying mechanisms remain unclear. Here, I report that GALNT3 suppresses lung cancer development and progression by inhibiting the tumor initiation as well as altering a tumor microenvironment (TME). This study suggests that GALNT3 reduces self-renewal abilities of lung cancer cells by regulating β-catenin expression, an important factor in the WNT signaling pathway. Furthermore, GALNT3 suppresses the infiltration of myeloid-derived suppressor cell (MDSC), which then subsequently reduces angiogenesis. Finally, I find that GALNT3 decreases S100A9 and CXCL1 mRNA levels and reduces Tumor Necrosis Factor α (TNFα)-induced NF-κB signaling activation, which potentially reduces MDSC recruitment into the tumors. Consequently, this study reveals a tumor-suppressive role of GALNT3 in lung cancer and suggests GALNT3 as a novel therapeutic target for lung cancer.