A polymethylmethacrylate fraction of molecular weight 2.63×10⁶ has been studied by viscosity and by light scattering in an iso-refractive solvent-non-solvent system, methyla-cetate-ethanol. The results show that dlog[η]/dlog√h²=3 as demanded by Flory-Fox's theoretical interpretation of intrinsic viscosity. It is shown that the solution viscosity has reached the region of Newtonian flow at low shear rates under the conditions of ordinary viscometric determinations. The composition of θ-solvent of the system at 25.0° has been found to be γ_ω (ethanol)=0.509. The molecular weight distribution of the sample was determined by the method of sedimentation velocity in ultracentrifuge at the vicinity of θ-temperature in acetone-ethanol.