This study reports the preparation and characterization of alkali-activated slag based geopolymer foamed material (GFM). The roles of rice husk ash (RHA) on thermal stability and thermal insulation of GFM were systematically investigated. Thanks to the low self-weight and good reactivity of RHA, the compressive strength and specific compressive strength of GFM are enhanced, promoting the lightweight and high-strength developments of GFM. More importantly, the replacement of GGBS by RHA efficiently mitigates the strength degradation, reduces the weight loss and increases the volumetric stability of GFM during thermal exposure. The thermal conductivity of GFMs registered from 0.1102-0.2891 W/m•K reflects good thermal insulation characteristic, which is better than the reported thermal insulation properties of other alkali-activated foamed materials system at the same strength/density level. The mechanism of RHA acting on GFMs is closely related to the property characteristics of RHA itself, basic properties enhancement and pore structure development of GFMs. With the use of 20 wt.% RHA, the GFM containing 2 wt.% H2O2 exhibits the optimal comprehensive properties: 0.01270 × 103kN•m/kg specific compressive strength, 827 kg/m3 volume density, 10.5MPa compressive strength, 0.1331 W/m•K thermal conductivity and better volumetric stability.