Some neutral cis- and trans-polyacetylene samples have been studied at 30 - 0.7 mm wave band EPR. A higher spectral resolution allows one to determine the principal values of anisotropic g-tensor of localized paramagnetic centers in polyacetylene, attributed to pinned neutral solitons. The very-high-frequency EPR allows us to observe the increase of a number of such centers and the appearance of soliton diffusion along the polymer chains after the cis-trans isomerization