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Commercial bacterial exopolysaccharide (EPS) applications have been gaining interest; therefore, strains that provide higher yields are required for industrial-scale processes. Succinoglycan (SG) is a type of bacterial anionic exopolysaccharide produced by <i>Rhizobium</i>, <i>Agrobacterium</i>, and other soil bacterial species. SG has been widely used as a pharmaceutical, cosmetic, and food additive based on its properties as a thickener, texture enhancer, emulsifier, stabilizer, and gelling agent. An SG-overproducing mutant strain (SMC1) was developed from <i>Sinorhizobium meliloti</i> 1021 through N-methyl-N′-nitro-N-nitrosoguanidine (NTG) mutation, and the physicochemical and rheological properties of SMC1-SG were analyzed. SMC1 produced (22.3 g/L) 3.65-fold more SG than did the wild type. Succinoglycan (SMC1-SG) overproduced by SMC1 was structurally characterized by FT-IR and ¹H NMR spectroscopy. The molecular weights of SG and SMC1-SG were 4.20 × 10⁵ and 4.80 × 10⁵ Da, respectively, as determined by GPC. Based on DSC and TGA, SMC1-SG exhibited a higher endothermic peak (90.9 °C) than that of SG (77.2 °C). Storage modulus (G′) and loss modulus (G″) measurements during heating and cooling showed that SMC1-SG had improved thermal behavior compared to that of SG, with intersections at 74.9 °C and 72.0 °C, respectively. The SMC1-SG′s viscosity reduction pattern was maintained even at high temperatures (65 °C). Gelation by metal cations was observed in Fe³⁺ and Cr³⁺ solutions for both SG and SMC1-SG. Antibacterial activities of SG and SMC1-SG against <i>Escherichia coli</i> and <i>Staphylococcus aureus</i> were also observed. Therefore, like SG, SMC1-SG may be a potential biomaterial for pharmaceutical, cosmetic, and food industries.