Dielectric properties along the grain for absolutely dried untreated and seven kinds of chemically treated Sitka spruce ( Picea sitchensis Carr.) woods were measured. Cole-Cole's circular arc law was applied to the results of the relaxation due to the motions of methylol groups. The following changes were caused by chemical treatments. In polyethylene glycol ( PEG) impregnation, the distribution of relaxation times became very narrow, the generalized relaxation time (tau(m)) was considerably decreased, and the relaxation magnitude (epsilon(0) - epsilon(infinity)) was slightly increased. In acetylation, the distribution of relaxation times became very broad, tm was considerably increased, and (epsilon(0) - e(infinity)) was remarkably decreased. In propylene oxide treatment, the distribution of relaxation times became slightly narrow and tm was decreased. tm was slightly decreased in formalization, phenol-formaldehyde (PF) resin treatment and wood methyl methacrylate (MMA) composite. (epsilon(0) - epsilon(infinity)) was decreased in formalization and PF-resin treatment and was hardly changed in wood-MMA composite and heat treatment. The distribution of relaxation times was almost unchanged in formalization, PF-resin treatment, wood-MMA composite and heat treatment. (C) 2003 Kluwer Academic Publishers.