Thermal Degradation and Flammability are two important specifications a composite material must passed for consideration of use in the building and construction industry application. Additives such as antioxidant (AO) and flame retardant (FR) are incorporated into the UPR/EPS composite mixture in this study to impart flammability resistance and improve its thermal decomposition characteristic. The composites thermal decomposition were characterized via Thermal Gravimetric Analyzer of 20% SBR with combinations of AO and FR additives. Flammability test were also performed to evaluate their linear burning rate. An increase in thermal stability was found for combined AO and FR additive system. A possible presence of synergistic mechanism contributing towards degradation resistance at high temperature range with combined AO and FR additives. High Residue % or Char Yield for the SBR AO and SBR AO FR systems may indicate that AO limits oxidative process and thus increases the char yield. The linear burning rate for the SBR-FR series were reduced by 60% by flame retardant incorporation. Hence, it was shown that addition of antioxidant and flame retardant additives had enhanced thermal stability of SBR/EPS/UPR composite system.