Samples and fractions of a membrane-forming polymer poly[1-(-trimethylgermyl)propyne], with the molecular weight within 4 < M × 10^-4 < 170 were studied in cyclohexane by methods of molecular hydrodynamics (centrifugal sedimentation, translational isothermal diffusion, and viscometry). The molecular-weight dependences of the hydrodynamic characteristics were determined and analyzed. These dependences were used to estimate the equilibrium rigidities of the poly[1-(trimethylgermyl)propyne] chains. The size of the macromolecules was studied as influenced by the bulk effects. The results obtained are compared with published data for poly[1-(trimethylsilyl)propyne].