Characterization of protein solutions is of great importance for biophysical research, pharmaceutical industry, and medicine. Particularly, the monitoring of the protein aggregation is crucial at all stages of biotechnological production and in the diagnosis of dangerous diseases. The present work is focused on a study of prospects and possibilities of NMR relaxation of solvent nuclei for monitoring the state of proteins in solutions. The spin–lattice and spin–spin relaxation rates (R₁ and R₂) of solvent nuclei were measured in the solutions of a small globular protein, RRM2 domain of TDP-43 protein. The solvent was either H₂O- or D₂O-based buffer with pH 6.5 and contained 20 mM sodium phosphate and 150 mM NaCl. The relaxation rates of the solvent ¹H, ²H, ²³Na, and ³⁵Cl nuclei in solutions of soluble and aggregated RRM2 domain of TDP-43 protein were studied. The aggregation was induced by mild oxidative stress, using treatment by hydrogen peroxide. It was found that aggregation of protein could be detected using NMR relaxation of ¹H nuclei. The observed CPMG dispersion for R₂ rates confirms the millisecond timescale for the hydrogen exchange between water and protein sites. The correlation times and binding constants for sodium and chlorine ions were estimated using concentration dependences for relaxation rates (²³Na, ³⁵Cl). The relaxation rates of solvent nuclei are sensitive to the presence of protein in solution even at low protein concentrations, and the relaxation rates of different nuclei reflect various aspects of the state of the protein.