Dimensional change of preserved waterlogged wood was studied as a function of relative humidity. The dimensional changes of specimens exposed to 1) cyclical change of relative humidity, 2) a constant dry condition, and 3) a constant humid condition, were measured by computerized data accumulation from strain gages. It was found that: 1) waterlogged wood, after preservation treatment, changes dimensionally like sound wood in response to relative humidity variation, although the degree of change is smaller and varies with the treatment; the difference between the tangential and radial dimensional changes varies with the treatment applied; 2) waterlogged wood treated with polyethylene glycol (PEG) has problems in both humid and dry conditions. In humid conditions, PEG weeps, although the wood swells a little. In dry conditions, the wood shrinks gradually and continuously to quite a large extent, perhaps causing it to crack. This shrinkage might result from the PEG rather than the wood.