Abstract: Fenugreek gum (FG), a naturally occurring galactomannan, is limited in its broader industrial utilization due to its relatively poor solubility in water. To address this, carboxymethylation was applied to improve its aqueous dispersibility, with the degree of substitution (DS) hypothesized as a critical factor influencing the modification outcomes. In this work, carboxymethylated fenugreek gum (CMFG) was synthesized via a wet-route approach, targeting DS values of 0.18, 0.52, and 0.87 by systematically tuning variables such as alkali concentration, reaction temperature, and etherifying agent dosage. Analytical results showed that molecular weights of CMFG were consistently lower than that of the unmodified FG, as observed via gel permeation chromatography. Congo red binding tests revealed an absence of triple-helix organization in all samples, suggesting disordered, coil-like conformations. The introduction of carboxymethyl groups was confirmed by distinct new peaks at 1421 cm⁻¹, 1322 cm⁻¹, and 1604 cm⁻¹ in the Fourier transform infrared spectroscopy (FTIR) spectra. Crystallinity and thermal resistance were both reduced upon modification, as indicated by X-ray diffraction (XRD) and thermogravimetric analysis (TGA) results. Despite these structural alterations, rheological measurements showed that carboxymethylation significantly improved the water solubility of FG. Among the samples, CMFG with a moderate DS of 0.52 (CMFG_0.52) exhibited the highest emulsifying activity (28.31±0.30 m²/g) and foaming capacity (32.17%±0.38%) at a concentration of 10 mg/mL, outperforming FG, CMFG_0.18 , and CMFG_0.87. These values were notably higher than those of FG and the other two modified variants, suggesting that excessive substitution might be counterproductive for interfacial activity. In summary, moderately substituted CMFG demonstrated an optimal balance between structural integrity and functionality, offering new insights into the design of soluble, bio-based polysaccharide materials for application in food and related industries.