Periodate oxidized dextran has been widely studied in a broad range of biotechnological applications, regardless of this, usually little attention is paid to the oxidation extension consequences on the properties of the final modified dextran. Based on a bidimensional NMR analysis, we suggest that the two aldehydes groups, resulting from the periodate oxidation, are not fully reactive with N-nucleophiles, under certain pH conditions. The aldehyde group bonded to C3 appeared to be the only prone to react. The other aldehyde might be arrested in more stable hemiacetal structures. The hemiacetals are also responsible for oxidized dextran crosslinking, interfering in simple processing steps, such as dissolution and solubility, as well as increasing the viscosity of the solutions. The molecular weight variation on the oxidized samples can be followed by dynamic mechanical thermal analysis in consequence of the variation of glass transition temperature with the molecular weight, which was corroborated by the onset temperature of the thermal degradation.