Properties of soluble polyetherimide samples are studied via molecular-hydrodynamics methods. According to the sedimentation–diffusion analysis, the molecular masses of the samples are in the range (5–65) × 10³ g mol^–1. Scaling ratios relating hydrodynamic characteristics to molecular mass are ascertained, and the conformational characteristics of polyetherimide molecular chains are determined. The statistical segment calculated from the translational- and rotational-friction data is 2.7 ± 0.7 nm. A comparison of this value with the statistical segment calculated for freely jointed chains yields a rotation-hindrance parameter of 1.16.