Diffusion of PVA through pores of an Al2O3 compact was measured by means of “diffusion from a stirred solution to a spherical compact powder”. The porosity and the diameter of the compact, and the volume of PVA aqueous solution did not markedly affect the measured value of diffusion coefficient within the region of the present study, thereby the diffusion coefficient of PVA in this system can be measured reproducibly by present method. The diffusion coefficient of PVA through pores in an Al2O3 compact was much smaller than that in a PVA aqueous solution. In the calculation of the diffusion coefficient, not only modification of the equilibrium PVA concentration in the sphere, but also modification of the pores through which PVA diffuses must be taken into account. Effect of adsorption of PVA on the apparent diffusion coefficient was discussed.