A new environment-friendly thermal insulation material binderless cotton stalk fiberboard (BCSF) made from cotton stalk fibers with no chemical additives was developed using high frequency hot-pressing. The goal of this paper was to investigate the effect of board density, fiber moisture content (MC) and pressing time on thermal conductivity and mechanical properties of BCSF. The results showed that the board with a density of 150-450 kg/m(3) had the thermal conductivity values ranging from 0.0585 to 0.0815 W/m K, which was close to that of the expanded perlite and vermiculite within the same density range. The thermal conductivity values had a strong linear correlation with the board density. The internal bonding strength (IBS) of boards was good at the relatively low-density level, which can be significantly improved with increasing the fiber MC and prolonging pressing time. The same trend was observed for modulus of rapture (MOR) and modulus of elasticity (MOE) of the boards. As an environment-friendly and renewable material, the BCSF is particularly suitable for ceiling and wall applications to save energy. (C) 2010 Elsevier B.V. All rights reserved.