Cross-linked hyaluronic acid (HA) hydrogels are used in many biomedical applications but their characterization in order to distinguish between physicochemical properties is challenging. Longitudinal (T1) and transverse (T2) relaxation times and diffusion coefficient (D) of water protons in diepoxide 1,4-butanediol diglycidyl ether (BDDE)-cross-linked HA hydrogels were analyzed by high-field NMR spectroscopy to distinguish between different physicochemical properties. Hydrogels of different degrees of modification and cross-linking, representing a range of gel content, swelling ability, elastic and viscous behavior were studied, as well as solutions of native HA of different molecular weights. T1, T2 and D were measured for several concentrations of HA and as a function of temperature. D and T1 showed a weak concentration dependence, but did not differ between the hydrogels. T2, dominated by chemical exchange between water protons and exchangeable protons of HA, varied significantly between the different hydrogels and the temperature profiles changed dramatically between different concentrations.