The effect of carboxymethylation on the functional and physicochemical properties of bambara groundnut starch was studied. The starch yield on the dry weight of the seed basis was 40.35%, degree of substitution was 0.78, while the reaction efficiency was 62.50%. The FTIR spectra confirmed the presence of the carboxymethylated group on the modified starch granule with new bands at 1590, 1455 and 1423 cm−1. X-ray diffractogram revealed the loss of crystallinity as a result of carboxymethylation of the starch. DSC study showed that the gelatinisation temperature and enthalpy were significantly altered by the carboxymethylation, also the pasting property corroborate this observation with the increase in the paste viscosity from 278.58 to 300.83 RVU. The solubility and swelling power of the native and carboxymethylated starch increased with increase in temperature, but with no significant effect on the swelling power of the starch in alkaline and acidic medium (pH 2–12).