This study was carried out to investigate the effect of heat-treatment and particle size on the crystalline properties of the wood cellulose. The color of wood flours was changed from light yellow in control sample to dark yellow or deep brown by heat treatment at 100℃ to 200℃. Relative crystallinity of the heat treated wood cellulose decreased with decreasing particle size from wood chips to 200 mesh, and there was little change in the crystal width. As the temperature was increased, relative crystallinity of the wood increased and crystal width was not changed. As a result of the FT-IR analysis, it was confirmed that the peaks were gradually decreased at -OH elongation as the heat-treated temperature was increased. The lignin C-H bending of 1425 cm -1 and the hemicellulose C-H bending of 1370 cm -1 did not change with the increase of the heat treatment temperature. In addition, it was revealed that C-C stretching of carbohydrate near 1031 cm -1 decreased with increasing heat treatment temperature. Consequently, it is suggested that particle size and heat treatment affected the crystalline properties of wood cellulose.