Abstract: A modified clay is provided, which includes a layered clay material intercalated with a modifier having a conjugated double bond and capable of producing free radicals when heated. A clay-polymer composite is also provided, which includes a polymer material and the modified clay, wherein the modified clay is dispersed in the polymer material and at least partially exfoliated. The modifier is capable of producing free radicals when heated to scavenge free radicals generated from thermal cracking or burning of the polymer material to prevent further thermal cracking of the polymer material.