In this report, study of diffusion phen-omena in concentrated solution of high polymeric substance was undertaken. Experiments were done using polyvinyl alcohol (P. V. A.) aqueous solutions, which contained NaOH and indicator, and were formed into semi-infinite medium. As H₂SO₄ was diffusing into this medium, mutual diffusion of H₂SO₄-NaOH with a clear moving boundary was observed. Relations between the position of boundary line (ξ) and time (t) were studied. The relations ofξ_??_√t were straight. From these results the diffusion constant in the polymer solution was calculated.
The mutual diffusion constant was decreased with increase of polymer content in solution, and its value was 1.07×10^-5cm²•sec^-1 in 17.0% PVA (DP 1150) solution, whereas in true solution, it was 1.5×10^-5 Cm²•sec^-1.