Inorganic geopolymer potassium aluminosilicate was prepared at room temperature by the reaction of kaolin, potassium silicate, and potassium hydroxide solution and was dispersed in situ into an epoxy rnatrix by various proportions to fabricate novel inorganic-organic hybrid geopolymer composites. The formation of inorganic geopolymer with respect to time was monitored by X-ray diffraction and FT-IR analysis and confirmed that 36 inin is required to complete the geopolyinerization. When geopolymers were properly mixed at different ratios with organic polymers such as epoxy and cured, these hybrid polymers exhibit significant thermal stability. Pure kaolin was also incorporated into the epoxy rnatrix to compare the change in chemical and thermal properties. Cone calorimetry results showed about 27% decreased in rate of heat release (RHR) on addition of 20% pure kaolin. However, about 57% of RHR was decreased on addition of only 20% geopolymer. Evaluation of CO, and CO were found to be minimum 2.0 and 0.7 kg/kg, respectively, for hybrid geopolymer composites compared to very high yield for epoxy at 3.5 kg/kg after 200 s of ignition. The current study shows that due to the high thermal stability of hybrid geopolymer composites, the novel hybrid geopolymer composites have the ability to be potential candidates to use in practical application where fire is of great concern. (C) 2005 Wiley Periodicals, Inc.