Abstract: The effect of hydrothermal treatment on the color and mechanical properties of reversibly thermochromic bamboo flour/plastic composites was studied. ESEM observation was used to explain surface microstructure of reverisibly thermochromic bamboo/plastic composites. Surface chemical composition and crystallinity were determined by FTIR and DSC respectively. The results show that hydrothermal treatment has a great influence on the properties of bamboo/plastic composites with the order of hydro-thermal treatment at 80 ℃ >water-bath treatment >heat treatment at 80 ℃. There are many cracks appearing on the surface, contact angles and mechanical properties decrease obviously, and the color of samples changes greatly after hydro-thermal treatment at 80 ℃. There are some small cracks appearing on the surface, and contact angles decrease a little after water-bath treatment at room temperature. The mechanical properties of the bamboo flour/plastic composites presents firstly increasing then decreasing and then increasing again, and the color of samples change more obviously after water-bath treatment. The surface is smooth and the color change a little, the contact angles turn bigger after heat treatment at 80 ℃. The results of FTIR and DSC indicate that the bamboo fibre and high density polyethelene (HDPE) molecular chain lead to degradation in some extent, and recrystallization of HDPE is found after heat treatment at 80 ℃, water-bath treatment and hydro-thermal treatment at 80 ℃.