Humidity controlled warm air treatment is a method to disinfest insects in wood and other organic materials used for historical buildings and/or art works.The infested object is warmed with humidity controlled air until its temperature reaches higher than 55°C and kept in this condition for several hours. In the present study,a 300 mm cube block of keyaki (Zelkova serrata),one side surface of which is uncovered and the others covered with Japanese lacquer "urushi"layer was treated according to a pre-set program of the warm air treatment in an environmental chamber. Temperature and strain on the surfaces with and without urushi layer were measured using thermocouples and strain gauges,respectively.The measured strains were compared with theoretically calculated strains,based on the linear coefficient of expansion and the shrinkage rate for a change in moisture content for wood. Tensile or compression strains were observed perpendicular or parallel to wood grain, respectively. Absolute values of measured strains increased with increase in temperature and diminished as temperature decreased.Maximum tensile strains were 1200-1600 μεfor both wood and urushi surfaces, and these values were four or five times larger than the maximum absolute values of compression strains. These maximum strains were approximately one-third of annual strain changes measured on parts in traditional wooden buildings.The measured strain was divided into two components caused by temperature change and by moisture content change.The former was the value of strain gauge attached on the surface and covered with aluminum foil for moisture isolation.The latter was obtained by substituting the temperature-caused strain from the strain without foil. The temperaturecaused strain was as similar as the theoretically calculated strain.The MC change-caused strain was significantly smaller than the theoretically calculated strain,even if the humidity condition was set to change the MC of 1.5%.The study suggests that the strain caused by MC change could be kept at smaller levels for both surfaces when temperature and humidity are controlled appropriately.