Streptococcus mutans (MTCC 497) was grown anaerobically in acidic Brain heart infusion (BHI) medium with 15 % sucrose to produce cell-bound and extracellular water-insoluble polysaccharide mutan. Fourier transformed infrared (FTIR) and 13C NMR studies revealed a mixed linkage of alpha-1-3 and alpha-1-6 mutan with a production yield of 1.8 g/L. Mutan has a branched structure with a molecular weight (Mw) of 5654 Da. Water-insoluble mutan was carboxymethylated at 0.93 degrees of substitution. FTIR spectra with characteristic peaks at 1603 cm(-1) and 1418 cm(-1) due to symmetric and asymmetric vibrations of the COOgroup confirmed carboxymethylation. Thermal gravimetric analysis showed that native mutan and carboxymethyl mutan exhibited higher thermal stability. Carboxymethylation enhanced solubility and antioxidative radical-scavenging activity. The in-vitro antioxidative radical scavenging analysis revealed 52 % and 47 % inhibition of DPPH and ABTS radicals.