Silicate blocks were produced from rice hull ash (RHA) derived sodium silicate, and physical properties and thermal conductivity of the blocks were investigated. A Sodium silicate solution was produced from RHA by solublizing the silica in 1 M NaOH at 100 degreesC, followed by filtering to remove the carbon residue. The silicate solution was then boiled at different heating rates to evaporate the water and produce highly porous thermal insulation blocks with varying densities. X-ray diffraction patterns demonstrated the amorphous nature of silicate blocks. FTIR spectra demonstrated the presence of the silicate network in the silicate. Block density, mechanical strength (the compressive force per unit area required to break the block), and thermal conductivity decreased with increasing heating rate. The block density, mechanical strength, and thermal conductivity of silicate blocks were 0.33-0.42 g.cm(-1), 145-196 N.cm(-2), and 0.103-0.128 W.m(-1).K-1, respectively. Data suggested that RHA could be used to produce thermal insulation materials as a substitute for asbestos and organic polymer materials.