Physicochemical properties of poly-l-lysine (PLL) hydrobromide were determined by molecular dynamics (MD) modeling and a variety of experimental techniques. Primarily, the density, the chain diameter, the monomer length, and the PLL molecule conformations were theoretically calculated. These results were applied for the interpretation of experimental data acquired for the PLL sample of average molar mass equal to 122 kg/mol. They comprised the diffusion coefficient, the hydrodynamic diameter, and the electrophoretic mobility of molecules determined for the ionic strength ranging from 2 × 10-5 to 0.15 M and pH 5.6. Using these data, the electrokinetic charge and the effective ionization degree of PLL molecules were determined as a function of ionic strength. Additionally, precise dynamic viscosity measurements for dilute PLL solutions were performed yielding the intrinsic viscosity, which decreased from 2420 to 120 for ionic strengths of 2 × 10-5 and 0.15 M, respectively. This confirmed that PLL molecules assume extended conformations in accordance with theoretical modeling. These data enabled to determine the molecule length, the chain diameter, and its effective molecule cross-section area for various ionic strengths. Therefore, it was concluded that the combined dynamic light scattering and viscosity measurements supplemented by MD modeling furnish reliable information about PLL macromolecule conformations in electrolyte solution. Besides the significance for basic science, the results obtained in this work can be exploited for precisely determining the molar mass of macroions.