Despite the recent research and medical advances, non-small cell lung cancer (NSCLC) remains the most diagnosed lung cancer subtype and the leading cause of cancer-related deaths. Lung adenocarcinoma (LUAD) is the most common NSCLC subtype with KRAS, GTPase, being the most frequent oncogene. KRAS-mutant LUAD is very aggressive, invasive, and resistant to most of the therapies, including chemotherapy. Cancer development strongly relies on cell proliferation and migration, which in turn requires an interaction with the extracellular matrix (ECM). The ECM is mainly composed of proteins and glycosaminoglycans (GAGs), which maintain tissue structure and regulate cell function. GAGs are known to modulate cellular functions mainly through their interactions with cytokines and growth factors (GFs). Particularly, sulfated GAGs, such as heparin, have been shown to enhance the binding of GFs and angiogenesis mainly by altering their sulfation patterns. In the current work, we assessed the effect of the sulfation of heparin-mimetic sulfated GAGs on the proliferative and tumorigenic characteristics of KRAS-mutant LUAD cells. Sulfated alginates (SulfAlg) shown earlier to have heparin-mimetic properties were synthesized with varying degrees of sulfation (DS=0, 0.8, 2.0 and 2.7) and their effects on KRAS-mutant LUAD cells were assessed using two-dimensional (2D) and three-dimensional (3D) culture systems. The effects of SulfAlg were studied on two KRAS-mutant cell lines, H1792 and MDA-F471, derived from human and murine respectively. The increase in the DS of mimetic GAGs had insignificant effects on the proliferation of H1792 grown in 2D, using MTT and trypan blue exclusion assays. The proliferation of MDA-F471 unlike H1792 cells grown in 2D significantly decreased with the increase in the DS of SulfAlg for the highest dose of polysaccharides (100 µg/mL) used as shown by trypan blue exclusion assay, but insignificant decrease using MTT assay at the two different concentrations. Moreover, the migratory abilities of H1792 and MDA-F471 decreased significantly with the increase in the DS (p<0.001), as shown by the wound healing assay. The increase in the DS significantly decreased the sphere formation unit and the area of spheres for both cell lines (p<0.001). In conclusion, the increase in the DS of heparin-mimetic SulfAlg reduces the proliferation, migration and the area of spheres for KRAS-mutant LUAD in vitro possibly by differential binding to GFs. SulfAlg may be suitable for applications in cancer therapy after further in vivo validation.