Effective mass diffusion over cell boundaries in a Taylor-Couette how system was investigated ranging from singly periodic wavy vortex flow to weakly turbulent wavy vortex flow by a salt-solution tracer technique. In order to determine experimentally the intercell mixing coefficient k(CB) between the neighbouring pairs of vortices, an appropriate model was formulated. As a result, k(CB) depends not only on Taylor number but also on axial wavelength with fluid viscosity. In the singly periodic wavy vortex flow region, the intermixing is enhanced by periodic fluctuations resulting from azimuthally travelling waves on the cell boundaries. With increasing Taylor number in the doubly periodic wavy vortex flow and weakly turbulent wavy vortex flow regions, the mixing characteristics go toward axial turbulent diffusion. In these two flow regions, the correlation between k(CB) and effective diffusion coefficient D-z based on an axial diffusion model has been obtained as D-z = 2 lambda k(CB).