AbstractIntrinsic viscosities [η], second and third virial coefficients A2 and A3, respectively, and mean square radius of gyration 〈RG2〉 of a polymer homologous series of narrow‐molecular‐weight‐distribution polystyrene samples in a molecular weight range of 2000 up to 24 · 106 were determined in toluene at 25°C by light scattering and viscometry measurements. The results are (3 · 104 < Mw < 24 · 106, Mw/Mn ≤ 1,3): These results were obtained by consideration of the limit of the dilute solution regime, the determination of zero‐shear rate intrinsic viscosities, and the molecular weight dependence of the refractive index increment dn/dc. It was found that dn/dc increases slightly up to Mw = 1,8 · 106. A comparison of the [η]−Mw‐relationship with literature data is given. In addition the unperturbed (theta) dimension parameters K0, 〈h2〉0/M, the characteristic ratio C∞, the steric factor σ, and the thermodynamic interaction parameter B were calculated from the modified Burchard‐Stockmayer‐Fixman procedure using polymolecularity correction and the results compared with experimental data from the literature.